Fix HostResolveImportedModule's current realm handling

If this is called as part of module script loading of a dependency, there is no current realm. But we don't actually need the current realm, except in the case of a top-level import() inside an event handler, in which case there *will* be a current realm. Rearrange the logic of the algorithm to only look at the current realm (or rather, current settings object) in that later case.

Also removes some vestigial base URL stuff, and camel-cases all the variable names.

Closes #8410.

Author: domenic

source

@@ -94860,9 +94860,7 @@ dictionary <dfn dictionary>PromiseRejectionEventInit</dfn> : <span>EventInit</sp
   <var>referringScript</var> and a <span>string</span> <var>specifier</var>:</p>
 
   <ol>
-   <li><p>Let <var>settingsObject</var> be the <span>current settings object</span>.</p></li>
-
-   <li><p>Let <var>baseURL</var> be <var>settingsObject</var>'s <span>API base URL</span>.</p></li>
+   <li><p>Let <var>settingsObject</var> and <var>baseURL</var> be null.</p></li>
 
    <li>
     <p>If <var>referringScript</var> is not null, then:</p>
@@ -94876,6 +94874,19 @@ dictionary <dfn dictionary>PromiseRejectionEventInit</dfn> : <span>EventInit</sp
     </ol>
    </li>
 
+   <li>
+    <p>Otherwise:</p>
+
+    <ol>
+     <li><p><span>Assert</span>: there is a <span>current settings object</span>.</p></li>
+
+     <li><p>Set <var>settingsObject</var> to the <span>current settings object</span>.</p></li>
+
+     <li><p>Set <var>baseURL</var> to <var>settingsObject</var>'s <span>API base
+     URL</span>.</p></li>
+    </ol>
+   </li>
+
    <li><p>Let <var>importMap</var> be an <span>empty import map</span>.</p></li>
 
    <li><p>If <var>settingsObject</var>'s <span data-x="concept-settings-object-global">global
@@ -96187,25 +96198,28 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
   agents must use the following implementation: <ref spec=JAVASCRIPT></p>
 
   <ol>
-   <li><p>Let <var>settings object</var> be the <span>current settings object</span>.</p></li>
-
-   <li><p>Let <var>referencing script</var> be null.</p></li>
+   <li><p>Let <var>moduleMap</var> and <var>referencingScript</var> be null.</p></li>
 
    <li>
     <p>If <var>referencingScriptOrModule</var> is not null, then:</p>
 
     <ol>
-     <li><p>Set <var>referencing script</var> to
+     <li><p>Set <var>referencingScript</var> to
      <var>referencingScriptOrModule</var>.[[HostDefined]].</p></li>
 
-     <li><p>Set <var>settings object</var> to <var>referencing script</var>'s <span>settings
-     object</span>.</p></li>
+     <li><p>Set <var>moduleMap</var> to <var>referencingScript</var>'s <span>settings
+     object</span>'s <span data-x="concept-settings-object-module-map">module map</span>.</p></li>
+    </ol>
+   </li>
 
-     <li><p>Set <var>base URL</var> to <var>referencing script</var>'s <span
-     data-x="concept-script-base-url">base URL</span>.</p></li>
+   <li>
+    <p>Otherwise:</p>
+
+    <ol>
+     <li><p><span>Assert</span>: there is a <span>current settings object</span>.</p></li>
 
-     <li><p><span>Assert</span>: <var>base URL</var> is not null, as <var>referencing script</var>
-     is a <span>classic script</span> or a <span>JavaScript module script</span>.</p></li>
+     <li><p>Set <var>moduleMap</var> to the <span>current settings object</span>'s <span
+     data-x="concept-settings-object-module-map">module map</span>.</p></li>
     </ol>
 
     <div class="example">
@@ -96223,33 +96237,30 @@ import "https://example.com/foo/../module2.mjs";</code></pre>
     </div>
    </li>
 
-   <li><p>Let <var>moduleMap</var> be <var>settings object</var>'s <span
-   data-x="concept-settings-object-module-map">module map</span>.</p></li>
-
    <li><p>Let <var>url</var> be the result of <span data-x="resolve a module specifier">resolving a
-   module specifier</span> given <var>referencing script</var> and
+   module specifier</span> given <var>referencingScript</var> and
    <var>moduleRequest</var>.[[Specifier]].</p></li>
 
    <li><p><span>Assert</span>: the previous step never throws an exception, because <span
-   data-x="resolve a module specifier">resolving a module specifier</span> must have been previously
-   successful with these same two arguments (either <a
+   data-x="resolve a module specifier">resolving a module specifier</span> must have been
+   previously successful with these same two arguments (either <a
    href="#validate-requested-module-specifiers">while creating the corresponding module script</a>,
    or in <span>fetch an import() module script graph</span>).</p></li>
 
    <li><p>Let <var>moduleType</var> be the result of running the <span>module type from module
    request</span> steps given <var>moduleRequest</var>.</p></li>
 
-   <li><p>Let <var>resolved module script</var> be <var>moduleMap</var>[(<var>url</var>,
+   <li><p>Let <var>resolvedModuleScript</var> be <var>moduleMap</var>[(<var>url</var>,
    <var>moduleType</var>)]. (This entry must <span data-x="map exists">exist</span> for us to have
    gotten to this point.)</p></li>
 
-   <li><p><span>Assert</span>: <var>resolved module script</var> is a <span>module script</span>
+   <li><p><span>Assert</span>: <var>resolvedModuleScript</var> is a <span>module script</span>
    (i.e., is not null or "<code data-x="">fetching</code>").</p></li>
 
-   <li><p><span>Assert</span>: <var>resolved module script</var>'s <span
+   <li><p><span>Assert</span>: <var>resolvedModuleScript</var>'s <span
    data-x="concept-script-record">record</span> is not null.</p>
 
-   <li><p>Return <var>resolved module script</var>'s <span
+   <li><p>Return <var>resolvedModuleScript</var>'s <span
    data-x="concept-script-record">record</span>.</p></li>
   </ol>
 
@@ -129531,6 +129542,7 @@ INSERT INTERFACES HERE
   Neil Rashbrook,
   Neil Soiffer,
   Nereida Rondon,
+  networkException,
   Nicholas Shanks,
   Nicholas Stimpson,
   Nicholas Zakas,