Improve instruction selector for mask and shift operations by using cheaper
instructions where possible, in preference to UBFX.

Reverted because it was suspected of causing a couple of flaky tests to fail,
but investigation suggests this is unlikely.

Original review: https://codereview.chromium.org/1677023002

BUG=

Review URL: https://codereview.chromium.org/1684073006

Cr-Commit-Position: refs/heads/master@{#33988}