This commit resolves an issue where using an uninstantiated generic type
parameter in a signal form model caused TypeScript compilation failures due to
distributive conditional types (angular#66596). The previous attempt to fix this issue
by tuple-wrapping everything caused another bug (angular#65535) that prevented property
access on generic unions.

This commit balances the need to resolve nested generic property access while
handling infinitely recursive generic structures without depth errors.

What changed and why:
- Base State Wrappers: Tuple wrappers (`[TModel] extends [AbstractControl]`) are
  applied to `FieldTreeBase` to safely defer generic evaluation. This prevents
  primitive unions (like `boolean`) from incorrectly evaluating to `never`.
- Naked Map Over Children: Object subfield checks (`TModel extends Record`) are
  re-evaluated as purely naked conditionals. Eager distribution over generics
  allows users to directly access shared properties of unresolved union types.
- Array Interface Deflection: `ReadonlyArrayLike<T>` generic abstraction is
  redefined as an explicit `interface` instead of a mapped `Pick` type alias.
  This optimally intercepts TypeScript from eagerly evaluating infinitely
  recursive array structures (e.g. `RecursiveType = (number | RecursiveType)[]`).
- Overloaded Context Methods: `FieldNodeContext.stateOf` and `fieldTreeOf` are
  defined as explicitly overloaded class methods and lexically bound (`this`) in
  the constructor. These changes are required to safely align the runtime bindings
  with the tautological conditionals implemented in the `RootFieldContext`
  interface structure.

Fixes angular#65535