don't use Clang modules in the "only re-export public symbols" check

[QuietMisdreavus]

Cherry-pick of #66610

• Explanation: When an underlying Clang module is present, the [-symbol-graph]-minimum-access-level flags for SymbolGraphGen are overridden by the "export-import only public symbols" check. This PR changes the latter check to require that symbols and export-imported modules come from the same compiler for the symbol to be considered re-exported.
• Scope: Affects users who want to view internal symbols in a symbol graph but also have Clang code in their project.
• Issue: rdar://110399757
• Risk: Low. The change in behavior should only affect underlying Clang modules; other behavior around export-imports should be unaffected, as is normal compilation.
• Testing: A test has been added to ensure that [-symbol-graph]-minimum-access-level continues to work as expected in the presence of an underlying Clang module. Existing tests continue to pass.
• Reviewer: @daniel-grumberg

[QuietMisdreavus]

@swift-ci Please test