[AA] Allow specifying REx file contents in testdata.

Tests can now specify the code generated by a resolve extension from
within the test's testdata. Module-level directives control whether
resolve extensions are enabled for that module, as well as package names
and source shadowing regexes. File-level directives allow a `// FILE:`
block within the testdata to be converted into a KtResolveExtensionFile
and removed from the module as a whole. (This requires a new
`ModuleStructureTransformer`, because we need to be able to entirely
remove the files in question.)

Any test can add support for these directives by calling
`KtResolveExtensionTestSupport.configure` from within their
`configureTest` stanza. This allows this functionality to be used in
conjuction with any test base class.

^KT-59329

generators/analysis-api-generator/tests/org/jetbrains/kotlin/generators/tests/analysis/api/analysisApi.kt

@@ -90,13 +90,9 @@ private fun AnalysisApiTestGroup.generateResolveExtensionsTests() {
                 frontendIs(FrontendKind.Fir) and
                 testModuleKindIs(TestModuleKind.Source)
     ) {
-        test(AbstractSingleModuleReferenceResolveWithResolveExtensionTest::class) {
+        test(AbstractReferenceResolveWithResolveExtensionTest::class) {
             model("referenceResolve")
         }
-
-        test(AbstractMultiModuleReferenceResolveWithResolveExtensionTest::class) {
-            model("multiModule/referenceResolve")
-        }
     }
 }