Generate lint and feature information on server start up instead of embedding them

We currently generate lints, clippy lints and unstable features at compile time every now and then and embed that into our executable. This list gets outdated over time until someone updates it again and it also relient on the compiler version of the person running the tests. We should remove this and query these lists when the server starts.

For rust lints we already use rustc itself to fetch the lints.

For the feature list we clone the rust repo, there doesn't currently seem to be any way to fetch features through rustup.

For rustdoc lints we already use rustdoc itself to fetch the lints.

For clippy lints we download the lints.json file from the rust-lang github page, I don't think there is a way for us to fetch the info we want from a user installation.

The test that generates the things is here:
https://github.com/rust-analyzer/rust-analyzer/blob/3632d5946f1cac47b7cba646a83b64eb9da0f878/crates/ide_db/src/tests/sourcegen_lints.rs

Start with crates/ide_db/src/tests/sourcegen_lints.rs to understand how the lint and feature lists are currently generated and embedded. Trace the existing rustc and rustdoc queries, the Rust repository feature lookup, and the clippy lints.json download. Done means these lists are obtained when the server starts rather than generated at compile time, with the relevant tests updated and passing.