Add support for `get` and `set` as shorthand properties. Also
supports them for CoverInitializedName in BindingPatterns and (once implemented)
AssignmentPatterns.

BUG=v8:4412, v8:3584
LOG=N
R=adamk, aperez, wingo, rossberg

Review URL: https://codereview.chromium.org/1328083002

Cr-Commit-Position: refs/heads/master@{#30769}