[arm64] Make ArgumentsAdaptorTrampoline maintain 16-byte stack alignment.

This is to help the transition to using CSP as the stack pointer.
It does not make JSSP aligned yet, just makes sure that we only modify
JSSP by a multiple of 16 bytes. To do this, we might need to add a padding
slot above the receiver.

BUG=

Review-Url: https://codereview.chromium.org/2938603002
Cr-Commit-Position: refs/heads/master@{#46030}