fix: Error when a type variable is unbound during monomorphization instead of defaulting to Field

[jfecher]

Description

Problem*

Resolves

Summary*

Adds an error when encountering an unbound TypeVariableKind::Normal instead of defaulting it to a Field.

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[michaeljklein]

LGTM

[michaeljklein]

• HirLValue's now all have both a Location and a Type
• LValueRhs's now all have a Span

@jfecher Would it make sense to factor out the common fields into a struct, e.g.

struct HirLValue {
  location: Location,
  typ: Type,
  kind: HirLValueKind,
}

?

[jfecher]

@jfecher Would it make sense to factor out the common fields into a struct, e.g.

Possibly. I'd like to keep it as the enum for now though since there's only 1-2 common fields and making these structs would prevent them from being matched on directly anymore.

[jfecher]

@vezenovm @michaeljklein I've found a case I missed where array lengths were defaulting separately to zero still. I've fixed this and added a test case. Requesting a re-review for these changes.