FEXCore/JIT: Encode the JITRIPReconstructionEntries using variable length integer

[Sonicadvance1]

When #2722 implemented this initially and #4271 switched over to signed int16_t there was assumptions made that int16_t was a reasonable trade-off in encoding size versus needing to deal with 8-bit values being too small in some cases.

In the common case we are almost always encoding 8-bit values because instructions are typically linear (and less than 15-bytes in size), but 16-bit was chosen because optimizing JIT and multiple instructions that don't cause exceptions can add up to larger than 8-bit.

Instead of hardcoding 16-bit values, implement a variable length integer class where ~96.8% of values are 8-bit encoded, and the remaining 3.19% are encoded using 16-bit. Due to some constraints that #4271 put in place, we can basically guarantee currently that branch targets are within 16-bit. The VL class does support 32-bit and 64-bit as well so if we change behaviour then nothing needs to change.

Some stats when running Sonic Mania with multiblock enabled.

Encoded integers: 3,504,907
Encoded 8-bit:    3,393,095 (96.8%)
Encoded 16-bit:     111,812 (3.19%)
Encoded 32/64-bit:        0

Encoded Size:       3,615,181 bytes (3.44MiB)
Fixed encoded size: 7,007,604 bytes (6.68MiB)

Definitely worth using and saves the headache of large RIP/PC offsets causing problems.