Remove `BFormTextarea` from `GlFormTextarea`
## [BootstrapVue props we should support](https://bootstrap-vue.org/docs/components/form-textarea#component-reference)
- `aria-invalid`
- `autocomplete`
- `autofocus`
- `debounce`
- `disabled`
- `id`
- `max-rows`
- `name`
- `no-resize`
- `placeholder`
- `readonly`
- `required`
- `rows`
- `size`
- `state`
- `trim`
- `value`
## [BootstrapVue props we should consider _not_ supporting](https://bootstrap-vue.org/docs/components/form-textarea#component-reference)
https://gitlab-org.gitlab.io/frontend/bootstrapvue-component-usage-breakdown/components.json can be used as a starting point to see if the prop is used, but should not be considered an exhaustive list (it does not check https://gitlab.com/gitlab-org/customers-gitlab-com/ or Switchboard, please do this manually). We should weigh the pros and cons of supporting each prop individually.
- `form`
- `formatter`
- `lazy`
- `lazy-formatter`
- `no-auto-shrink`
- `number`
- `plaintext`
- `wrap`
## [BootstrapVue events we should support](https://bootstrap-vue.org/docs/components/form-textarea#comp-ref-b-form-textarea-events)
- `blur`
- `change`
- `input`
- `update`
issue