Fix findAllReferences for export= namespace with ES6 imports

[mag123c]

Fixes #62348

This fixes findAllReferences for the export = namespace + ES6 import pattern.

Problem

When using:

export = React;
declare namespace React { function lazy(): void; }
import { lazy } from "./mod";

Find All References doesn't work.

Solution

Added fallback symbol resolution in findAllReferences.ts for import specifiers when standard resolution fails.

Testing

Added test case findAllReferencesExportEqualsNamespace.ts. All existing tests pass

[mag123c]

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