[clang] [clang][ASTImporter] Add import of node 'FileScopeAsmDecl' (PR #193244)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat approved this pull request.

As in your other PR (#193492), I'm giving a weak LGTM on this commit.

As I'm not an expert on ASTImporter it would be nice to wait for a better review (e.g. from @ojhunt or @shafik?), but I think you can merge this PR if you don't get another review relatively soon.

https://github.com/llvm/llvm-project/pull/193244