Behind the --wasm-inlining flag, we introduce speculative direct calls
as an alternative to invoking functions through references.
In pseudocode, call_ref(func_ref, args...) reduces to
  if (func_ref == function_reference_at(expected_index)) {
    call_direct(expected_index, args...)
  } else call_ref(func_ref, args...)
The introduced direct call can later get inlined in WasmInliningPhase.
Currently, we always speculate that the reference is the function at
index 0. Proper heuristics, based on liftoff runtime feedback, will come
later.

Bug: v8:12166, v8:7748
Change-Id: Icd1319d3091b436e71906717fd8a2662bfbb8481
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3162602
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76884}