feat(directive): validate input transforms like ngtsc

[ashley-hunter]

Stack (2/4): #493 inputs/outputs → #494 transform validation → #495 queries: → #496 .d.ts transform types. This is #494.

Checks input transforms the way ngtsc does, for both @Input({ transform }) and inputs: [{ transform }].

The bug

ngtsc rejects a transform it can't prove is a usable function (parseDecoratorInputTransformFunction). oxc accepted anything, so code that fails to build with ngc compiled here, e.g.

const toNumber = (v: string) => Number(v);

@Directive({ selector: '[d]' })
export class D {
  @Input({ transform: toNumber }) value!: number;   // ngtsc: Input transform must be a function
}

The fix

Each rule matches ngtsc, with its diagnostic word for word and in its order (inputs: entries, then members):

• not a function: literals, classes, calls, and function expressions reached through a variable, property access or parentheses (only one written directly as the property value is analyzable)
• generic, or overloaded: more than one call signature
• first parameter: untyped, a spread, or typed with a same-file type that isn't exported
• name clash: a static ngAcceptInputType_<name> member already on the class

The evaluator learns functions to do this: same-file function declarations and static methods resolve to their definitions. A transform reached through such a reference (T.f where const T = { f }) is emitted as the function's own name, as ngtsc does.

One deliberate difference: for a static method (transform: Utils.coerce) ngtsc emits the bare method name. That name isn't in scope, so it either throws or binds an unrelated same-named function, and oxc keeps the written expression instead.

@Input members are also recognised through a namespace import (@core.Input), like @core.Component already was. Imported transforms can't be inspected from one file and are assumed to be functions.

Tests

Added to the ngtsc snapshot: Angular's input transform specs from ngtsc_spec (non-function values, generic, overloaded, spread, untyped, non-exported type, ngAcceptInputType clash), plus probes of each rule and of how ngtsc describes values in these errors. The three ngtsc_spec cases that need types from another file are listed as skipped with that reason, as is an aliased @Input import (member decorators are matched by name throughout oxc). A separate test covers the static-method case.