[llvm] [ValueTracking] Improve `Bitcast` handling to match SDAG (PR #125935)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

https://zig.godbolt.org/z/PWqzTGd31 - should be able to replace both psll intrinsics (currently only one)

https://github.com/llvm/llvm-project/pull/125935