fix various const eval errors
These were found after const_evaluating arbitrary expressions and linting if the const evaluator failed
fixes#33275 (int -> float casts for negative ints)
fixes#33291 (int -> char casts (new! wasn't allowed in constants until this PR))
r? @eddyb
cc @bluss @japaric
match check: note "catchall" patterns in unreachable error
Caught as catchall patterns are:
* unconditional name bindings
* references to them
* tuple bindings with catchall elements
Fixes#31221.
The extra filename and line was mainly there to keep the indentation
relative to the main snippet; now that this doesn't include
filename/line-number as a prefix, it is distracted.
There was no span available in the cast function, but we need to infer the `x` in `x as char` to `u8`.
The spans are now removed from all functions using `infer` and instead added in `eval_const_expr_partial`
Automated conversion using the untry tool [1] and the following command:
```
$ find -name '*.rs' -type f | xargs untry
```
at the root of the Rust repo.
[1]: https://github.com/japaric/untry
