Strings aren't supported in switch statements

[mattjohnsonpint]

Bug description

You should be able to use a switch statement for variables that are of type string, but it currently gives compiler errors:

This was mentioned lightly in #648 (comment) but I'll call it out as a bug.

Steps to reproduce

export function test(s: string): string {
  switch (s) {
    case 'foo':
      return 'abc';
    case 'bar':
      return 'def';
    default:
      return 'ghi';
  }
}

ERROR TS2322: Type '~lib/string/String' is not assignable to type 'u32'.
   :
 2 │ switch (s) {
   │         ~
   └─ in assembly/index.ts(2,11)

ERROR TS2322: Type '~lib/string/String' is not assignable to type 'u32'.
   :
 3 │ case 'foo':
   │      ~~~~~
   └─ in assembly/index.ts(3,10)

ERROR TS2322: Type '~lib/string/String' is not assignable to type 'u32'.
   :
 5 │ case 'bar':
   │      ~~~~~
   └─ in assembly/index.ts(5,10)

FAILURE 3 compile error(s)
Build failed.

A nullable string (ie. string | null) should also work, with null being a valid case, but fails in the same manner.

Workaround

Use consecutive if statements:

export function workaround(s: string): string {
  if (s === 'foo') {
    return 'abc';
  }
  if (s === 'bar') {
    return 'def';
  }
  return 'ghi';
}

... but this shouldn't be mandatory.

AssemblyScript version

v0.27.36