Bug 252209

rdar://100332177

The current default WebAssembly baseline JIT is based on emitting Air instructions. This is a moderate compile-time improvement over emitting B3, but still isn't very fast and generates relatively inefficient code. WebAssembly should lend itself relatively well to faster and simpler compilation methods, and we should be able to improve both startup speeds and generated code quality in the baseline JIT by transitioning to a single-pass baseline compiler.

Core design principles:
 - Don't waste time generating an IR, emit instructions directly.
 - Generate decent but not optimized code. We can do better than spilling everything to stack slots, but we shouldn't do liveness analysis or optimization passes.
 - Emphasize compilation speed via efficient data structures and straightforward code generation.

This is the parent bug for all subcomponents of this feature. The initial patch is tracked in https://bugs.webkit.org/show_bug.cgi?id=250052, and we'll make additional bugs to track additional features/fixes as needed.