`incompatible_msrv`: lint function calls with any argument count

The lint for function calls was previously restricted to functions taking
exactly one argument. This was not documented.

Generalizing the lint to an arbitrary number of arguments in the function
call requires special casing some macro expansions from the standard
library. Macros such as `panic!()` or `assert_eq!()` exist since Rust
1.0.0, but modern stdlib expand those macros into calls to functions
introduced in later Rust versions. While it is desirable to lint code
inside macros, using MSRV-incompatible functions coming from `core`
in macro expansions has been special-cased to not trigger this lint.

Also, code coming from compiler desugaring may contain function calls
(for example, `a..=b` is now desugared into `RangeInclusive::new(a,
b)`. Those should not be linted either as the compiler is allowed to
use unstable function calls.

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