gdbstub: Dynarmic only supports ARM breakpoints, not Thumb

[DimitriPilot3]

Opcode for a bkpt 0 ARM instruction: 0xE1200070 (little endian bytes: 70 00 20 E1)
Opcode for a bkpt 0 Thumb instruction: 0xBE00 (little endian bytes: 00 BE)

Currently, GDBStub::CommitBreakpoint hardcodes the ARM opcode in so that the JIT/Dynarmic gets simple breakpoint support through the CPU exception handler. However, one can't expect GDBStub to guess if the target code is in ARM-mode or Thumb-mode: if guessed wrong, then it'll corrupt the code and cause unexpected behaviour. (We could look for odd addresses ending in 2, 6, A, or E, but this would merely be a hack / an edge case.)

Fortunately, as long as not more than 1 instruction is corrupted, DynCom / interpreter wouldn't care anyway, as it uses GDBStub::GetNextBreakpointFromAddress after each dispatch to predict when it's about to hit a breakpoint.

Idea: move the logic of installing a bkpt 0 opcode out of CommitBreakpoint and RemoveBreakpoint, and into the JIT somehow.