Port 81a1530e

Original commit message:

    Before frame elision, we finalized the frame shape when assembling the
    prologue, which is also when we prepared the frame (saving sp, etc).

    The frame finalization only needs to happen once, and happens to be
    actually a set of idempotent operations. With frame elision, the logic for
    frame finalization was happening every time we constructed the frame.
    Albeit idempotent operations, the code would become hard to maintain.

    This change separates frame shape finalization from frame
    construction. When constructing the CodeGenerator, we finalize the
    frame. Subsequent access is to a const Frame*.

    Also renamed AssemblePrologue to AssembleConstructFrame, as
    suggested in the frame elision CR.

    Separating frame setup gave the opportunity to do away with
    architecture-independent frame aligning (which is something just arm64
    cares about), and also with stack pointer setup (also arm64). Both of
    these happen now at frame finalization on arm64.

R=mtrofin@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=
LOG=N

Review URL: https://codereview.chromium.org/1903343002

Cr-Commit-Position: refs/heads/master@{#35674}