Document memory64 wasm proposal as having tier 1 support (#10159)

* [x] [Continuous fuzzing][fuzz1], and tested [to get fuzzed][fuzz2]
  * [x] [Custom fuzz target][fuzz-target]
* [x] Implementation ready to have CVEs assigned if necessary.
* [x] Reasonable to expect most developers to assist in maintenance.
* [x] RFC required for future changes affecting APIs/implementation.
* [x] [Stage 4 WebAssembly proposal](https://github.com/WebAssembly/proposals)
* [x] No known bugs/open questions.
* [x] [Available in Wasmtime API][rust-api]
* [x] [Available in Wasmtime C API][c-api]

[fuzz1]: https://github.com/bytecodealliance/wasmtime/blob/e60b6e623bca1203cf4b9c844254c25ccebe9d6d/crates/fuzzing/src/generators/module.rs#L49
[fuzz2]: https://github.com/bytecodealliance/wasmtime/blob/e60b6e623bca1203cf4b9c844254c25ccebe9d6d/crates/fuzzing/src/oracles.rs#L1311
[fuzz-target]: https://github.com/bytecodealliance/wasmtime/blob/e60b6e623bca1203cf4b9c844254c25ccebe9d6d/crates/fuzzing/src/oracles/memory.rs#L20-L23
[rust-api]: https://docs.rs/wasmtime/latest/wasmtime/struct.MemoryTypeBuilder.html#method.memory64
[c-api]: https://docs.wasmtime.dev/c-api/memory_8h.html#a3db783fad4992c3f6985c92274b14ad7

Author: alexcrichton

docs/stability-tiers.md

@@ -38,6 +38,7 @@ For explanations of what each tier means see below.
 | WebAssembly Proposal | [`multi-memory`]                           |
 | WebAssembly Proposal | [`threads`]                                |
 | WebAssembly Proposal | [`tail-call`]                              |
+| WebAssembly Proposal | [`memory64`]                               |
 | WASI Proposal        | [`wasi-io`]                                |
 | WASI Proposal        | [`wasi-clocks`]                            |
 | WASI Proposal        | [`wasi-filesystem`]                        |
@@ -71,7 +72,6 @@ For explanations of what each tier means see below.
 | Target               | `s390x-unknown-linux-gnu`  | Continuous fuzzing          |
 | Target               | `x86_64-pc-windows-gnu`    | Clear owner of the target   |
 | Target               | Support for `#![no_std]`   | Support beyond CI checks    |
-| WebAssembly Proposal | [`memory64`]               | Unstable wasm proposal      |
 | WebAssembly Proposal | [`function-references`]    | Unstable wasm proposal      |
 | WebAssembly Proposal | [`wide-arithmetic`]        | Unstable wasm proposal      |
 | Execution Backend    | Pulley                     | More time fuzzing/baking    |