wgsl switch spec grammar allows case default

[simonbuchan]

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

switch_statement :
| switch expression brace_left switch_body + brace_right

switch_body :
| case_clause

| default_alone_clause

case_clause :
| case case_selectors colon ? compound_statement

default_alone_clause :
| default colon ? compound_statement

case_selectors :
| case_selector ( comma case_selector ) * comma ?

case_selector :
| default

| expression

the body is a list of [switch_body]s, which can be either case [case_selectors] ... or default ..., but [case_selector] can also be default, meaning, if I'm reading this correctly, should allow both:

switch x {
  default { foo }
  case 1 { bar }
}

and

switch x {
  case default { foo }
  case 1 { bar }
}

but the latter on naga (0.10.0) gives something like:

Shader 'box.wgsl' parsing error: expected unsigned/signed integer literal, found 'default'
   ┌─ wgsl:60:12
   │
60 │       case default { uv.x = 0.0; }
   │            ^^^^^^^ expected unsigned/signed integer literal

    expected unsigned/signed integer literal, found 'default'