Describe the PR

New <b-sidebar> component, for creating fixed viewport (left or right) slide out drawers.

Users can place any arbitrary content they wish in the sidebars.

Very basic component, that leaves the majority of styling and content layout up to the user.

Roughly based on the Bootstrap offcanvas example.

Closes #3324
Closes #3210
Closes #1702

To Do:

• make header with close button optional
• optional footer slot
• accessibility docs
• lazy prop docs
• unit testing
• SASS variables
• other stuff (TBD)
  • close on ESC keypress (opt-out)
  • close on route change (opt-out) uses fullPath including query and hash
  • add optional lazy content rendering
  • handle tooltips/popover inside sidebars
  • close on clickout/focusout? (opt-in or out ? as it may close on things like interactive popovers) leaving out for now.
  • add docs page for v-b-toggle directive (make a separate PR)

PR checklist

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

• Bugfix
• Feature
• Enhancement
• ARIA accessibility
• Documentation update
• Other (please describe)

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

• No
• Yes (please describe)

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 #xxx[,#xxx]), where "xxx" is the issue number)
• It 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.
• The title should follow the Conventional Commits naming convention (i.e. fix(alert): not alerting during SSR render, docs(badge): update pill examples, chore(docs): fix typo in README, 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)
• Includes any needed TypeScript declaration file updates
• New/updated tests are included and passing (if required)
• Existing test suites are passing
• CodeCov for patch has met target
• 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)