Fix https://github.com/llvm/llvm-project/issues/132059.
Providing incorrect mappings via `-fmodule-file=<name>=<path/to/bmi>`
can crash the compiler when loading a module that imports an
incorrectly mapped module.
The crash occurs during AST body deserialization, when the compiler
attempts to resolve remappings using the `ModuleFile` from the
incorrectly mapped module's BMI file.
The cause is an invalid access into an incorrectly loaded
`ModuleFile`.
This commit fixes the issue by verifying the identity of the imported
module.