In an initial attempt to implement sloppy mode lexical bindings,
functions were made lexically scoped in sloppy mode. However, the
ES2015 spec says that they need an additional hoisted var binding,
and further, it's not clear when we'll implement that behavior
or whether it's web-compatible.

This patch splits off function block scoping into a new, separate
flag called --harmony_sloppy_function. This change will enable the
possibility of testing and shipping this feature separately from
other block scoping-related features which don't have the same risks.

BUG=v8:4285
R=adamk
LOG=N

Review URL: https://codereview.chromium.org/1282093002

Cr-Commit-Position: refs/heads/master@{#30122}