`infer` emits duplicate TypeScript type names

[zharinov]

infer can generate two type declarations with the same name. The output is invalid TypeScript.

Case 1: enum labels that differ only by case

cargo run -p plotnik -- infer -l javascript -q 'Q = [Foo: (identifier) FOO: (number)]'

export interface QFoo { $tag: "Foo"; }
export interface QFoo { $tag: "FOO"; }   // duplicate name
export type Q = QFoo | QFoo;

Labels Foo and FOO both map to the name QFoo.

Case 2: explicit annotation collides with a generated name

cargo run -p plotnik -- infer -l javascript -q 'Q = {(identifier) @foo :: QBar { (number) @x } @bar}'

export interface QBar { x: Node; }
export type QBar = Node;                  // duplicate name

The explicit type name QBar on @foo and the name generated for the @bar scope are the same.

Expected

Type names must be unique. Either disambiguate colliding names, or reject the query with a diagnostic.