Lint against `panic!(format!(...))` and `assert!(..., format!(...))`

[RalfJung]

What it does

assert! and panic! have built-in support for formatting, but they also accept arguments of type String, so one could use format! instead.

Using format! here is entirely unnecessary, and yet happens in the wild, so this seems like a useful target for a Clippy lint. Also the long-term plan is to not support String arguments any more, so such code might not work in future editions.

Cc @m-ou-se

Example

panic!(format!("hello {}", var))
assert!(x, format!("hello {}", var))

Could be written as:

panic!("hello {}", var)
assert!(x, "hello {}", var)

[m-ou-se]

It will probably be very soon that rustc itself has a lint for panic!(not-a-string-literal) and assert!(expr, not-a-string-literal) (to warn about the potential upcoming edition change), so it might not be worth it to add this to Clippy now.

[giraffate]

related issue: #5013

[giraffate]

#3155 is also a related issue.

[camsteffen]

Added in #7743