TypeScript improvements (#477)

* Change MockInstance generics to unknown

* Replace all any generics with unknown

* Don't allow explicit any by default

* Allow linting before build

* Use explicit return type rather than any

* Remove unneeded @types/jest types import

Author: keeganwitt

.eslintrc

@@ -51,9 +51,7 @@
       "plugins": ["@typescript-eslint"],
       "extends": ["plugin:@typescript-eslint/recommended"],
       "rules": {
-        "@typescript-eslint/array-type": "error",
-        // should probably enable this, but it's a bit too strict for now
-        "@typescript-eslint/no-explicit-any": "off"
+        "@typescript-eslint/array-type": "error"
       }
     }
   ]

all.js

@@ -1 +1,3 @@
+// override rule to allow running linting before build (dist directory won't exist yet)
+/* eslint import/no-unresolved: "warn" */
 require('./dist/all');