[CallPromotionUtil] See through function alias when devirtualizing a virtual...

[CallPromotionUtil] See through function alias when devirtualizing a virtual call on an alloca. (#80736)

- Extract utility function from
`DevirtModule::tryFindVirtualCallTargets` [1], which sees through an alias to a function. Call this utility function in
the WPD callsite.
- For type profiling work, this helper function will be used by indirect-call-promotion pass to find the function pointer at a specified vtable offset (an example in [2])

[1] https://github.com/llvm/llvm-project/blob/b99163fe8feeacba7797d5479bbcd5d8f327dd2d/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp#L1069-L1082
[2] https://github.com/minglotus-6/llvm-project/blob/77a0ef12de82d11f448f7f9de6f2dcf87d9b74af/llvm/lib/Transforms/Instrumentation/IndirectCallPromotion.cpp#L347