So far, initializer-expression evaluation was tied to setting global
values. We now need it to operate independently of globals, so that we
can implement new constant expressions like struct.new, which need their
arguments to be computed before they can be initialized.

Changes:
- Move type computation of WasmInitExpr into WasmInitExpr::type.
- Fix WasmInitExpr::type kRttSub case for rtts without depth.
- Introduce InstanceBuilder::EvaluateInitExpression().
- Rename InstanceBuilder::GetRawGlobalPointer() ->
  GetRawUntaggedGlobalPointer().
- Simplify InstanceBuilder::InitGlobals using EvaluateInitExpression().
- Introduce ValueType::is_numeric.
- Add Simd128(byte*) constructor.
- Introduce WasmValue::CopyTo() for numeric types.

Change-Id: Ic502b611f3998187abd9fc6ec377c2954c27abdc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2939982
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74949}