Previously SharedTurboAssembler was a base class for ia32 and x64
TurboAssembler. This made it easy to share code, only if the
implementation was the same. In some cases, like
ExternalReferenceAsOperand, the implementation defers slightly between
the two architectures.

We add a new class template SharedTurboAssemblerBase,
which derives from SharedTurboAssembler. Using the CRTP pattern, we
can call derived classes functions using the template parameter.
For any function that is exactly the same, we can declare them in
the header and define them in the cc file, instead of inlining
them all into the header.

Bug: v8:11589
Change-Id: I9319bd0c26c76995cef43ae5ec3f69392b3f825b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3097109
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76469}