Replace PROP_TYPE_* constants with native JS constructors
## Summary
Replace all `PROP_TYPE_*` constant usages (e.g. `PROP_TYPE_STRING`, `PROP_TYPE_NUMBER`) with their native JavaScript constructor equivalents (`String`, `Number`, `Boolean`, `Array`, `Object`, `Function`, etc.) across the vendored BootstrapVue codebase.
This is a follow-up to https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/work_items/3391, which refactored `makeProp()` calls. Now that `makeProp()` is being removed, the `PROP_TYPE_*` constants it relied on can also be eliminated in favour of the native JS types that Vue 2 already accepts directly.
For each batch, also check whether any `PROP_TYPE_*` imports become **entirely unused** after the replacement and remove those imports too.
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## Batched rollout plan
### Batch 1: Mixins: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5914
- `mixins/dropdown.js`
- `mixins/form-control.js`
- `mixins/form-custom.js`
- `mixins/form-options.js`
- `mixins/form-size.js`
- `mixins/form-state.js`
- `mixins/form-text.js`
- `mixins/id.js`
### Batch 2: Form: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5926
- `components/form/form.js`
- `components/form/form-text.js`
### Batch 3: Table helper mixins used by components: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5915
- `components/table/helpers/**`
### Batch 4: Table: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5916
- `components/table/*.js`
### Batch 5: Button: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5917
- `components/button/*.js`
### Batch 6: Dropdown: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5918
- `components/dropdown/*.js`
### Batch 7: Tabs: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5919
- `components/tabs/*.js`
### Batch 8: Modal: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5920
- `components/modal/*.js`
### Batch 9: Tooltip: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5921
- `components/tooltip/*.js`
### Batch 10: Form-Group: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5922
- `components/form-group/*.js`
ignoring the reducer which will be part of col.js and form-row.js refactoring
### Batch 11: Popover: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5924
- `components/popover/*.js`
### Batch 12: Form-Select: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5927
- `components/form-select/*.js`
### Batch 13: Form-Textarea: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5925
- `components/form-textarea/*.js`
### Batch 14: Transition and Transporter: https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/merge_requests/5923
- `components/transition/*.js`
- `components/transporter/*.js`
### Final batch:
- Remove PROP_TYPE_X constants which can be removed now
issue