Optimize Pre-compilation Format

[chadhietala]

In the compiled output we currently send down a lot strings that get mapped into runtime syntax objects. While this works and is an extremely large improvement over Glimmer1's output we still have headroom here for further optimizations.

In the short term we should keep an enum in Glimmer that maps an opcode name to a string. In the long term we may want to investigate going further down the byte-array path.