Read-only memory optimizations

This came up in the context of thinking about how to optimize file system calls, but it could be more generally useful. The idea is to tell Binaryen what memory is read-only, essentially telling it where the .rodata section is. Then optimizations like precompute and constant propagation would be able to resolve loads from that memory at compile time. This could particularly help for precomputing string operations like strlen and strcmp when their arguments are constant strings.

Start by reading the issue proposal and its references to Binaryen optimizations such as precompute and constant propagation. No files, tests, or entry points are named, so first determine where memory information and these optimizations are represented. Done would require an agreed design and support for resolving loads from declared read-only memory, including the cited constant-string cases.