fix: merge reactive inject from provide mixins

[seekskyworld]

Issue link: #13005

Summary:

• merge reactiveInject descriptors when provide options from mixins are combined
• add regression coverage for reactive inject from mixins

Motivation:

• prevent reactive inject entries from being overwritten when multiple mixins provide them

Validation:

• pnpm test:unit -- test/unit/features/options/inject.spec.ts