Tracking issue for shared memory

[abrown]

This issue tracks anything incomplete with the effort to add shared memories started in #4187:

• wasm-smith: generate shared memory when --threads is present wasm-tools#624
• fuzz: allow generating shared memories #4266
• improve tests (@alexcrichton had a comment about trying to stress things by doing more in Wasm)
• add a SharedMemoryType to the wasmtime external API (@alexcrichton wanted this to disambiguate entirely between memories and shared memories
• enable shared memory in the C API (Extend C API with interfaces needed to use threads #7940)
• shared memory: use shared memories with the pooling allocator #4244
• shared memory: no way to report memory growth failure #4240
• shared memory: audit safety of pointer copies in the presence of shared memories #4203
• shared memory: allow threads and memory64 proposals to coexist #4267
• shared memory: enable shared memory in differential_v8 fuzz target #4268
• Growth/creation of a shared memory is not subject to resource limiters
• Shared memories are disabled by default in Wasmtime
• Pulley's reconcilation with shared memories may or may not have holes (unsure)
• Behavior of wait/notify aren't customizable Epoch interruption of memory.atomic.wait* instructions #12809