`wasm-bindgen` no longer works with feature resolver version 1

[dtolnay]

$ cargo +stable new repro --edition=2018
$ cd repro
$ cargo +stable add wasm-bindgen@=0.2.96   # =0.2.95 works
$ cargo +stable check
...
error[E0554]: `#![feature]` may not be used on the stable release channel
 --> ~/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wasm-bindgen-macro-0.2.96/src/lib.rs:4:5
  |
4 |     feature(allow_internal_unstable),
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
For more information about this error, try `rustc --explain E0554`.
error: could not compile `wasm-bindgen-macro` (lib) due to 1 previous error

$ rustc +stable --version --verbose
rustc 1.83.0 (90b35a623 2024-11-26)
binary: rustc
commit-hash: 90b35a6239c3d8bdabc530a6a0816f7ff89a0aaf
commit-date: 2024-11-26
host: x86_64-unknown-linux-gnu
release: 1.83.0
LLVM version: 19.1.1

[dtolnay]

Bisects to 83c9deb (#4284). @daxpedda

[daxpedda]

I added a CI check so this doesn't happen again.
Fixed in #4306.

[daxpedda]

So I had to dig into this a bit more, because apparently no [target.'cfg(...)'.dependencies] table worked correctly unless specifying the target. So that means no target_feature and no cfg flag. I found out that the issue can be solved by just using resolver = "2".

While I was working in #4306 to fix this issue without requiring resolver = "2", there are some interactions that can't be easily addressed and overall it makes the situation much worse. So I'm tending towards just requiring resolver = "2".

Any input would be appreciated!