Add a --maglev-inlining flag, and add some half-baked support for
inlining functions when there is call feedback.

When the flag is enabled and there is call feedback, we create a nested
MaglevGraphBuilder for the current graph, and pause building the graph
of the outer function. We manually set up its prologue to set up its
frame with the arguments pass into the call, build the body with the
nested graph builder. This inner builder knows that it is building an
inlined function, and all Return bytecodes will instead emit a Jump to a
single merge block at the end of the function, where execution of the
outer function can resume.

These inner function basic blocks are wired into the outer graph with
new JumpToInline and JumpFromInline control nodes. The idea is that
subsequent passes will know what the inline function is, and will use
these to manage the function stack (particularly for codegen and
especially deopts).

Bug: v8:7700
Change-Id: I4e9b153f8cf4d06c56e7be6365e7a18b86a773c0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3585958
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Linke <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80077}