Replace rustc_semver with rustc_session::RustcVersion

[Alexendoo]

Allows dropping a dependency but there is a behaviour change here, the following versions are no longer accepted:

• 1 (would need to be 1.0 or 1.0.0)
• 1.0.0-alpha
• 1.0.0-alpha.2
• 1.0.0-beta

But this seems unlikely to effect anybody, I did some GitHub searching and found no occurrences outside our UI tests

r? @flip1995

changelog: none

[Jarcho]

Is there any reason for us to store the whole version? An MSRV of 1.30.1 would be the same as 1.30 for us since patch releases don't add new features. An MSRV of 2.0 or higher would mean we can't lint anything anyways since there's no guarantees that any of current rust works the same.

[Alexendoo]

Mostly it's that storing the version as is makes the implementation simple, we could get away with just storing the minor version for the current MSRVs

It's not impossible that we'd want to gate some suggestion on a bugfix in the future though

[flip1995]

RIP rustc-semver 🥲 I wrote this crate in the hope that Clippy, cargo and rustc can all use it. But then, everyone rolled their own implementation. So I think unifying Clippy version with the rustc implementation is a good idea.

@bors r+

[bors]

📌 Commit b32a017 has been approved by flip1995

It is now in the queue for this repository.

[bors]

⌛ Testing commit b32a017 with merge 52192aa...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 52192aa to master...