Replace arrayIncludes utility with native Array.prototype.includes
## Summary
Replace all usages of the `arrayIncludes()` utility function from the vendored BootstrapVue codebase with the native JavaScript equivalent — `Array.prototype.includes()` (e.g. `['a', 'b', 'c'].includes(value)`).
This is part of the broader [Remove BootstrapVue](https://gitlab.com/groups/gitlab-org/-/work_items/15178) effort. The `arrayIncludes` helper is an unnecessary abstraction over a method that is natively available in all supported environments.
For each batch, also check whether the `arrayIncludes` import becomes **entirely unused** after the replacement and remove it too.
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## Batched rollout plan
### Batch 1: `components/table/**`
All files under the table component directory that use `arrayIncludes`.
### Batch 2: `components/**`
All remaining files under the components directory (excluding `components/table/**` already covered in Batch 1) that use `arrayIncludes`.
### Batch 3: `mixins/**`
All files under the mixins directory that use `arrayIncludes`.
### Batch 4: `utils/**`
All files under the utils directory that use `arrayIncludes`.
Delete function itself, and tests if there are any
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