[CodeGen](NFC) Add `AliasAnalysis.h` to the CodeGen PCH (#227683)
After #226533, `MachineScheduler.h` no longer transitively includes
`AliasAnalysis.h` meaning its contents was dropped from the CodeGen PCH.
As such, a number of CPP files end up pulling it in manually and
regressing the size of TUs size significantly (see [this
comparison](https://llvm-compile-time-tracker.com/compare_clang.php?from=05a75e831476a8446d9319f56ce46851da86fb68&to=91b08a503f4f712ea8ce83dc3887f8be7738e95a&stat=instructions%3Au&sortBy=absolute-difference)).
Add `AliasAnalysis.h` to the CodeGen PCH to avoid this issue.
Thanks to @aengelke for pointing this out.