assessor: handle escaped quotes in MOF GetValue (#1276)

The MOF format escapes inner double quotes as " inside quoted string
values. The previous GetValue() implementation searched for the next '"'
literally, which truncated values like:

    DesiredObjectValue = "{"mountPoint":"/tmp"}";

to just '{\' before the JSON parser ever saw them. The compliance
engine then fell back to a key=value parser, which rejected '{' as a
key character and emitted "Invalid key: only alphanumeric and underscore
characters are allowed" once per rule with structured parameters.

Walk the string instead, honouring " and \ escape sequences, so a
JSON-encoded DesiredObjectValue arrives at UpdateUserParameters() in
its original unescaped form.

Co-authored-by: copilot <copilot@local>

Author: robertwoj-microsoft

src/modules/complianceengine/src/assessor/Mof.cpp

@@ -20,12 +20,32 @@ string GetValue(const std::string& line)
     {
         return std::string();
     }
-    const auto end = line.find('"', start + 1);
-    if (end == std::string::npos)
+    // Walk from the opening quote, honouring \" and \\ escape sequences so
+    // that MOF string values like "{\"key\":\"val\"}" are returned
+    // unescaped as {"key":"val"} instead of being truncated at the first
+    // inner quote.
+    std::string result;
+    size_t pos = start + 1;
+    while (pos < line.size())
     {
-        return std::string();
+        if (line[pos] == '\\' && pos + 1 < line.size())
+        {
+            const char next = line[pos + 1];
+            if (next == '"' || next == '\\')
+            {
+                result += next;
+                pos += 2;
+                continue;
+            }
+        }
+        else if (line[pos] == '"')
+        {
+            break;
+        }
+        result += line[pos];
+        ++pos;
     }
-    return line.substr(start + 1, end - (start + 1));
+    return result;
 };
 } // anonymous namespace