Auto merge of #140717 - mejrs:diagnostic_lints, r=oli-obk

Split up the `unknown_or_malformed_diagnostic_attributes` lint

This splits up the lint into the following lint group:
- `unknown_diagnostic_attributes` - triggers if the attribute is unknown to the current compiler
- `misplaced_diagnostic_attributes` - triggers if the attribute exists but it is not placed on the item kind it's meant for
- `malformed_diagnostic_attributes` - triggers if the attribute's syntax or options are invalid
- `malformed_diagnostic_format_literals` - triggers if the format string literal is invalid, for example if it has unpaired curly braces or invalid parameters
- this pr doesn't create it, but future lints for things like deprecations can also go here.

This PR does not start emitting lints in places that previously did not.

## Motivation

I want to have finer control over what `unknown_or_malformed_diagnostic_attributes` does

I have a project with fairly low msrv that is/will have a lower msrv than future diagnostic attributes. So lints will be emitted when I or others compile it on a lower msrv.

At this time, there are two options to silence these lints:

-  `#[allow(unknown_or_malformed_diagnostic_attributes)]` - this risks diagnostic regressions if I (or others) mess up using the attribute, or if the attribute's syntax ever changes.
- write a build script to detect the compiler version and emit cfgs, and then conditionally enable the attribute:
    ```rust
    #[cfg_attr(rust_version_99, diagnostic::new_attr_in_rust_99(thing = ..))]`
    struct Foo;
    ```
    or conditionally `allow`  the lint:
    ```rust
   // lib.rs
   #![cfg_attr(not(current_rust), allow(unknown_or_malformed_diagnostic_attributes))]
   ```

I like to avoid using build scripts if I can, so the following works much better for me. That is what this PR will let me do in the future:
```rust
    #[allow(unknown_diagnostic_attribute, reason = "attribute came out in rust 1.99 but msrv is 1.70")]
    #[diagnostic::new_attr_in_rust_99(thing = ..)]`
    struct Foo;

Author: bors