Changes:
- Merge all immediates which read a u32_v index into IndexImmediate.
  Refactor overloaded Validate(const byte*, [Type]Immediate) functions
  to Validate[Type](const byte*, IndexImmediate).
- Move MemoryIndexImmediate/MemoryAccessImmediate validation into their
  own Validate functions. Remove CheckHasMemory(), move its
  functionality into these Validate() functions.
- Refactor MemoryInitImmediate, TableInitImmediate and
  CallIndirectImmediate as composite immediates.
- Change field initializations for some Immediates to constructor
  initializers. This helps us drop some useless default constructors.
- Use the correct pc in StackEffect for struct.new_default.

Bug: v8:11831
Change-Id: I878f69a33f8473dc275184995b3b7b88fe0dfc8a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2928498Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74948}