The ES2016 draft spec defines a sort of fast path for constructing
a TypedArray based on another TypedArray. This patch implements that
alternative path in TypedArray construction. It is verified by
test262 tests, which now pass. This patch also has a slight cleanup
of TypedArray code by using a macro for TypedArray type checks, as
is done for other types.

This patch includes a minor spec violation: In the same-type case, the
spec indicates that the underlying ArrayBuffer should be copied until
the end, and this is fixed up by making the [[ArrayLength]] shorter.
This is observable with the buffer getter. This patch just copies the
used part of the underlying ArrayBuffer.

R=adamk
BUG=v8:4726
LOG=Y

Review URL: https://codereview.chromium.org/1754593003

Cr-Commit-Position: refs/heads/master@{#34443}