[clang] [clang][ASTImporter] Support Importer of BuiltinBitCastExpr (PR #74813)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

Can you please update the description to explain the problem in more details and why these changes fixes the problem. The description is what ends up in the git log and it is important that those logs provide enough information to understand the changes without having to view the details.

https://github.com/llvm/llvm-project/pull/74813