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

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 commented:

The change itself looks good. The major discussion happens on testing. So I don't have additional comments.

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