…Dylan-DPC

Document rounding for floating-point primitive operations and string parsing

The docs for floating point don't have much to say at present about either the precision of their results or rounding behaviour.

As I understand it[^1][^2], Rust doesn't support operating with non-default rounding directions, so we need only describe roundTiesToEven.

[^1]: rust-lang#41753 (comment)
[^2]: llvm/llvm-project#8472 (comment)

This PR makes a start by documenting that for primitive operations and `from_str()`.

…otriddle

Add new eslint rule to prevent whitespace before function call paren

It prevents `foo ()` basically. :)

r? `@notriddle`

…idtwco

Lifetime variance fixes for rustc

rust-lang#97287 migrates rustc to a `Ty` type that is invariant over its lifetime `'tcx`, so I need to fix a bunch of places that assume that `Ty<'a>` and `Ty<'b>` can be unified by shortening both to some common lifetime.

This is doable, since many lifetimes are already `'tcx`, so all this PR does is be a bit more explicit that elided lifetimes are actually `'tcx`.

Split out from rust-lang#97287 so the compiler team can review independently.

…rrors

Add some regression tests for rust-lang#90400

This adds two regression tests taken from rust-lang#90400 (comment).
Note that we cannot close the issue right now as the [original code](rust-lang#90400 (comment)) still triggers an ICE.

r? `@compiler-errors`