Add a new wasm32-wasip1 target to rustc

This commit adds a new target called `wasm32-wasip1` to rustc.
This new target is explained in these two MCPs:

* https://github.com/rust-lang/compiler-team/issues/607
* https://github.com/rust-lang/compiler-team/issues/695

In short, the previous `wasm32-wasi` target is going to be renamed to
`wasm32-wasip1` to better live alongside the [new
`wasm32-wasip2` target](https://github.com/rust-lang/rust/pull/119616).
This new target is added alongside the `wasm32-wasi` target and has the
exact same definition as the previous target. This PR is effectively a
rename of `wasm32-wasi` to `wasm32-wasip1`. Note, however, that
as explained in rust-lang/compiler-team#695 the previous `wasm32-wasi`
target is not being removed at this time. This change will reach stable
Rust before even a warning about the rename will be printed. At this
time this change is just the start where a new target is introduced and
users can start migrating if they support only Nightly for example.

compiler/rustc_target/src/spec/mod.rs

@@ -1575,6 +1575,7 @@ supported_targets! {
     ("wasm32-unknown-emscripten", wasm32_unknown_emscripten),
     ("wasm32-unknown-unknown", wasm32_unknown_unknown),
     ("wasm32-wasi", wasm32_wasi),
+    ("wasm32-wasip1", wasm32_wasip1),
     ("wasm32-wasip2", wasm32_wasip2),
     ("wasm32-wasi-preview1-threads", wasm32_wasi_preview1_threads),
     ("wasm64-unknown-unknown", wasm64_unknown_unknown),