FIx constant pool construction and throw correct exception on overflow.

[aardvark179]

@gbrail this should deal with the problems you saw related to #2461 and I was seeing on my const and loop fix branch. I've put it as a separate PR because I don't know what order you want to make these changes in.

[gbrail]

I'm happy to bring this in before the larger fix, but there are opportunities to make this change a bit more robust if we can.

[gbrail]

My AI friend's is convinced that 65535 is not a valid index even though it would pass this test because of the way that we often compute or store itsTopIndex + 1. (And FWIW we seem to +2 it a lot as well.) That would imply a different check here. A unit test to verify the duplication or non-duplication here would probably answer for sure.

[gbrail]

It's also a fair point that we make this overflow check in setConstantData but not in other places that allocate handles, including addConstant and others.

[gbrail]

Is the goal here to put the calculated value of "index" back in the "itsConstantHash" table? It doesn't appear that we do.

[aardvark179]

Okay, I got my robot friend to generate a bunch of unit tests and then do a more extensive rewrite. I moved all the indices to be ints to avoid the types of conversion errors we have previously seen. I think there is much more comprehensive refactoring and API change lurking in there which might help significantly improve class file compilation speed (profiling suggests we spend a large amount of the time repeatedly building and finding things like TypeInfo structures), but that's not a change to do right now.

[aardvark179]

I've added some simple class splitting to handle large scripts and emit a size exception if we emit too many invokeDynamic instructions in a single class (which seems to be the cause of the three.js problems. It works on the spot level of scripts, and cannot split large single nodes, or individual large methods, so compilation can still fall back to the interpreter for some scripts. three.js now successfully compiles to class files in the benchmarks.