Allow negative TransIDs in certain contexts

Summary: For the new inlining stuff, we need to be able to convert negative
BlockIds into nontrivial ProfSrcKeys, so that we can correctly track the
set of instructions that need interpreting, but without changing the
behavior of anything else.

We're already using JIT::BlockIds and TransIDs in a very transparent
manner, so let's just give them the same types and logical ranges.

Reviewed By: @ottoni

Differential Revision: D1444737
Check !typeMightRelax in simplifyConvObjToBool()

Reviewed By: @alexmalyshev

Differential Revision: D1635364
Move all inlining work to translateRegion()

Summary: Rather than inlining from the tracelet selector (or, more generally,
making the inlining decision in any particular region selector), let's
instead move the entire process into the translation path.  This gives
us inlining support for all regions, and is just generally nicer:

- We can, and have, turned off inlining for profiling translations.  The
  hottrace selector will still support inlining, since it does its own
  decision-making on the stitched-together region, but profiling
  translations are back to being single-block.

- Part of the inlining decision involves inspecting the callee's region,
  and inspecting a fully-formed region seems cleaner than looking
  through a region-that-has-been-formed-up-until-the-FCall-hopefully.

First-order inlining for hottrace regions may also allows us to inline
more calls in cases where we have more information.

The most prominent change to note is that inlined callees' blocks are no
longer included in the caller's region; instead, we just skip emitting
the FCall in HhbcTranslator and emit the callee region instead.

Because we no longer see the in-callee uses of types for profiling
tracelets, we duplicate the inlining decision-making during profiling
translations, and if a callee is inlinable, we constrain the types of
all of its arguments, to avoid losing out on an inlining opportunity.

Reviewed By: @swtaarrs

Differential Revision: D1428014