MIPS: Reland r20974: Unify and simplify the FastCloneShallowArrayStub.

MIPS: Reland r20974: Unify and simplify the FastCloneShallowArrayStub.

Port r21230 (56ef3ac)

Original commit message:
- Don't bake in length/capacity into full codegen calls of stubs,
allowing boilerplates to increase their capacity without regenerating
code.
- Unify all variants of the clone stub into a single,
length-independent version.
- Various tweaks to make sure that the clone stub doesn't spill and
therefore need an eager stack frame.
- Handle all lengths of array literals in the fast case.

BUG=

[Paul Lind, 2014-05-09 17:27:57]

lgtm

[Paul Lind, 2014-05-09 17:30:34]

Committed as r21239.