Allow reusing Scope temp variables

[pettyjamesm]

Allows temp variables to be reused within the same Scope instance after being released. This allows relatively smaller method bytecode sizes by using relatively fewer variable slots- which becomes significant since:

• accessing variable slots 0 - 3 is a single bytecode operation: aload_0, aload_1, aload_2, aload_3
• accessing variable slots 3 - 255 takes two bytes: aload <index>
• accessing variable slots 256+ takes 4 bytes: wide aload <two byte index>

Similar overheads are incurred when storing values into a variable, and for other non-reference type load/store bytecode operations.

[pettyjamesm]

@electrum / @dain PTAL

[dain]

Nice. I was going to add this years ago and never got to it :)