We create a ExternalReferenceAsOperand helper function in
SharedTurboAssemblerBase that delegates to the actual arch specific
implementation of TurboAssembler, because the ia32 and x64
ExternalReferenceAsOperand differs slightly in their implementation.

Bug: v8:11589
Change-Id: I378ea6b72fb2bba1a37482cc31cd58db0ba35721
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3114604Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76494}