Type conversions are not applied to switch selectors

[andyleiserson]

Description
Type conversions are not applied to switch selectors. Example (from https://math.hws.edu/graphicsbook/demos/c9/diffusion-demo.html, via https://bugzilla.mozilla.org/show_bug.cgi?id=1863457):

Shader '' parsing error: invalid switch value
   ┌─ wgsl:40:18
   │
40 │             case 0 {
   │                  ^ expected unsigned integer
   │
   = note: suffix the integer with a `u`: `0u`

(The error message suggests but does not explicitly show that the selector has type u32. I verified this to be the case.)

https://www.w3.org/TR/WGSL/#switch-statement says:

Type rule precondition: For a single switch statement, the selector expression and all case selector expressions must be of the same concrete integer scalar type.

and

The expressions in the case_selectors must be const-expressions.

This seems a bit underspecified, but we can probably do something reasonable.

[jamienicol]

I think this should have been fixed by #7250 ?

[andyleiserson]

I thought I had seen this somewhere... and I did search before I filed it 😕.

I will re-test with that fix.

[andyleiserson]

Verified that the sample in the description, and a couple others that I had linked to this issue, are fixed by #7250. I have updated them to link to #7225 instead.