Unifies the global and unallocated variable type accesses given that
--global_var_shortcuts is going away. Lda/StaGlobal is modified to use
Load/StoreICs on the global object. The named LoadIC and StoreIC bytecodes
are also modified so that they take a constant pool entry index for the
name rather than a register, avoiding unecessary LdaConstant bytecodes to
be emitted.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1419003002

Cr-Commit-Position: refs/heads/master@{#31482}