[clang] [CIR] Use SymbolTableCollection in LoweringPrepare's getCalledFunction (PR #195919)

[Erich Keane via cfe-commits]

erichkeane wrote:

> mlir::SymbolTableAnalysis stores this as attached ScopedSymbolTable to module I believe, which even survives between passes.

One thing I would like ot see is how we can keep it in 'sync' when we make changes.  It seems the symbol tables need to be manually updated, right? This feels error prone.

https://github.com/llvm/llvm-project/pull/195919