Adopt inject() over constructor DI (deferred until after 22.0.0)

[DuncanFaulkner]

Summary

Migrate the library from constructor parameter injection to the inject() function, using Angular's schematic:

ng generate @angular/core:inject

This is deferred until after the 22.0.0 release — it's a purely internal/stylistic refactor with no consumer-facing behavior change, and folding it into the release would mix a large mechanical refactor with functional changes.

Scope in this codebase

• 23 directives extend the abstract BaseDirective2, each calling super(elRef, styleBuilder, styler, marshal).
• 32 @Inject(TOKEN) sites across 5 secondary entry points: core, flex, extended, grid, server.
• BaseDirective2 (core/base/base2.ts) has a protected constructor with parameter-property deps and is exported from the public API (core/public-api.ts), so it's a consumer extension point.

Risks / caveats (why this needs care, not fire-and-forget)

1. Inheritance + super(...) — when the base drops constructor params, all 23 super(...) calls must change in lockstep. The schematic can leave a partial migration across entry points that needs manual cleanup.
2. BaseDirective2 is public + abstract — removing its constructor params is a breaking change for any downstream app that subclasses it and calls super(...). If migrating it, run the schematic in backwards-compatibility mode so a compatible protected constructor is retained (or treat it as an intentional, documented breaking change for the next major).

Acceptance

• Run ng generate @angular/core:inject in a dedicated PR (not the release PR)
• Manually reconcile the BaseDirective2 hierarchy / super() calls
• Decide & document the public abstract base handling (backwards-compat vs. breaking)
• Full test suite green (currently 468 tests) to confirm no behavior change

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