[clang] [clang][ASTImporter] Link FunctionDecl into its DeclContext before importing its body (PR #214009)

[Balázs Benics via cfe-commits]

steakhal wrote:

I resign from review. This area falls outside my interest. My goal was to challenge putting the tests into the clang static analyzer (CSA) parts because IMO these ASTImporter fixes affect a broader set of users and while having some CSA tests is beneficial, that shouldn't be the place for housing the bulk of the tests.
Historical data underpins this assumption. My voice is not authoritative of course - this is just my weak opinion - which applies to all ASTImporter patches.

@balazske and others should review this patch, along with the rest of the ASTImporter patches.

https://github.com/llvm/llvm-project/pull/214009