Type mismatch diagnostic suggests to append integer literal suffix to non-literal `const` expressions

[ErichDonGubler]

Repro steps

1. Run the following in Naga, i.e., cargo run -p naga ../in.wgsl:

   const my_unsigned_int: u32 = 1u;
   
   @compute @workgroup_size(1, 1, 1)
   fn main() {
       let my_signed_int: i32 = 1i;
   
       switch (my_signed_int) {
           case my_unsigned_int: {
               break;
           }
       }
   }

   Observe that the following error message is returned:

    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.37s
     Running `target\debug\naga.exe ../in.wgsl`
Could not parse WGSL:
error: invalid switch value
  ┌─ ../in.wgsl:8:14
  │
8 │         case my_unsigned_int: {
  │              ^^^^^^^^^^^^^^^ expected signed integer
  │
  = note: remove the `u` suffix: `my_unsigned_in`


error: process didn't exit successfully: `target\debug\naga.exe ../in.wgsl` (exit code: 1)

Expected vs observed behavior

We definitely shouldn't suggest this unless the expression is a single literal. We might adjust it by suggesting a constructor, i.e., i32(…), instead when there is something more complicated than a single literal present.

[ErichDonGubler]

Note: The premise of this PR is being invalidated somewhat, because #7250 will remove the offending diagnostic. However, the desired outcome of this issue is the same: Let's add hints that make sense for these errors.

[ErichDonGubler]

This issue is now subsumed by #7293.