Write release notes for 18.0.0

[alexcrichton]

Will backport after landing on main

[pchickey]

Because github doesn't allow multi-line suggestions, the changelog for wasi-common should be tweaked:

* Support for the old `wasi-common` crate and the original implementation of
  "WASIp1" aka "preview1" is being deprecated in the `wasmtime-wasi` crate.
  Users should migrate to the  `wasmtime_wasi::preview2` implementation, which
  supports both WASIp1 and WASIp2, as in the next release the
  `wasi-common`-based reexports of `wasmtime-wasi` will be deleted.
  [#7881](https://github.com/bytecodealliance/wasmtime/pull/7881)

[alexcrichton]

Updated 👍

[krn-sebastiaan]

Because github doesn't allow multi-line suggestions, the changelog for wasi-common should be tweaked:

It does, click on the blue +-sign and drag down until the desired line.

Dragging up won't work.

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