Make new stack_overflow test more tolerant

In contbuild it's failing on line 5 instead of 6.

Differential Revision: D937472
Improve error message for post-try blocks which are not finally

Currently, hhvm interprets post-try blocks not necessarily
beginning with an actual finally token as finally blocks, and thus
produces an error message to the user telling them finally blocks
are disabled even if they misspelled something, for example.

This moves things so the "finally disabled" message only comes up
if you enter a syntactically valid finally block.

Differential Revision: D918867
Add DataTypeProfiler

You can use this anywhere to sample the DataTypes at a particular
point in the code, for example calls to JIT helpers.

Differential Revision: D925193
Prerequisites for eager execution of async functions

Here's a few minor changes in emitter that will be needed later for
eager execution of async functions. Just to make the upcoming diff
sipmler.

Differential Revision: D935301
Rename VectorTranslator to MInstrTranslator

Vector has become too overloaded in this codebase. MInstrTranslator is
more accurate anyway; we have multiple different types of hhbc opcodes with
immediate vectors that aren't m-instrs.

Differential Revision: D935859
Implement ReflectionParameter::IsCallable()

The Facebook SDK unit tests fataled because ReflectionParameter::IsCallable() was not implemented. So, this implements it. Now the unit tests pass. Bad zend test now passes!

closes #931

Differential Revision: D938769
Optimize string same() and hitStringKey()

Most strings used as keys are either small or not shared, where the
data pointers cannot be equal.  Of the rest (shared), most could have
been small.

This diff copies small SharedVariant strings, so they don't refer
back to the SharedVariant, and don't need to be enlisted.  Then,
this changes hitStringKey() to not check data pointers, making it
equivalent to StringData::same().  Lastly, hand-write the comparison
loop in StringData::same() so we compare words at a time, and the
loop can be inlined.

Differential Revision: D937233
Parser refactorings: onFunction/onMethod/onClosure

We have separate methods for parsing functions and methods
(onFunction/onMethod), which have a lot in common. On the other
hand, onClosure just calls onFunction with a special parameter
that modifies its behavior. Lets make this more consistent and
remove the duplicated code.

Differential Revision: D934034