Description of Pull Request:

Migrates b-form-checkbox, b-form-radio, b-form-checkbox-group, and b-form-radio-group to use provide and inject for grouping detection.

• Moves common code and render functions into mixins (reducing code base)
• Adjusts custom-control structure to align with BS V4.1.3 new structure
• Adds inline prop to form-checkbox and form-radio (Closes Standalone checkboxes/radios are always inline by default #2234)
• Adds better support for b-form-radio to be used standalone mode (non group)
• Supports button mode in standalone mode (non group)
• New test suites using vue-test-utils

TODO:

• validate form-checkbox functionality
• validate form-radio functionality
• validate form-checkbox-group functionality
• validate form-radio-group functionality
• form-checkbox tests
• form-radio tests
• form-checkbox-group tests
• form-radio-group tests
• documentation updates

PR checklist:

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Enhancement to an existing feature
• ARIA accessibility
• Documentation update
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact:

The PR fulfills these requirements:

• It's submitted to the dev branch, not the master branch
• When resolving a specific issue, it's referenced in the PR's title (i.e. fixes #xxxx[,#xxxx], where "xxxx" is the issue number)
• The PR should address only one issue or feature. If adding multiple features or fixing a bug and adding a new feature, break them into separate PRs if at all possible.
• PR titles should following the Conventional Commits naming convention (i.e. "fix(alert): not alerting during SSR render", "docs(badge): Updated pill examples, fix typos", "chore: fix typo in docs", etc). This is very important, as the CHANGELOG is generated from these messages.

If new features/enhancement/fixes are added or changed:

• Includes documentation updates (including updating the component's package.json for slot and event changes)
• New/updated tests are included and passing (if required)
• Existing test suites are passing
• The changes have not impacted the functionality of other components or directives
• ARIA Accessibility has been taken into consideration (does it affect screen reader users or keyboard only users? clickable items should be in the tab index, etc)

If adding a new feature, or changing the functionality of an existing feature, the PR's description above includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)