goalc: Get CodeTester tests passing on Arm64 (only targetting macOS atm) (#3290)

This PR does the following:
- Designs a mechanism by which arm64 instructions can be encoded and
emitted
- Dispatch our higher-level instruction emitting calls to either x86 or
arm64 instructions depending on what the compiler is set to (defaults to
x86)
- Bare minimum scaffolding to get the arm64 instructions successfully
executing atleast on apple silicon
- Implement enough instructions to get the codetester test suite passing
on arm

test/goalc/test_game_no_debug.cpp

@@ -5,7 +5,7 @@
 #include "test/goalc/framework/test_runner.h"
 
 TEST(Jak1NoDebugSegment, Init) {
-  Compiler compiler(GameVersion::Jak1);
+  Compiler compiler(GameVersion::Jak1, emitter::InstructionSet::X86);
   compiler.run_front_end_on_string("(build-kernel)");
   std::thread runtime_thread = std::thread(GoalTest::runtime_with_kernel_no_debug_segment);