Added HTML5-PHP test suite

Summary: Closes #3042

Reviewed By: @fredemmott

Differential Revision: D1407665

Pulled By: @JoelMarcey
cellToBool, simplifyConvArrToBool, tvCastToBooleanInPlace don't match on NVTW

Summary: simplifyConvArrToBool and cellToBool call ArrayData::empty(), but
tvCastToBooleanInPlace has a comment saying it is intentionally
calling ArrayData::getSize() and having PHP5-incompatible behavior for
NVTW. This diff changes the first two to match the third.

Reviewed By: @oyamauchi

Differential Revision: D1406933
Fix cgIsScalarType assuming its argument is not const

Summary: Causes a test to fail with the simplifier disabled.

Reviewed By: @bertmaher

Differential Revision: D1406946