feat(icons): optional icon components

[tmorehouse]

Describe the PR

Opt in optional icon components.

Preview: https://deploy-preview-4489--bootstrap-vue.netlify.com/docs/icons/

Currently Bootstrap Icons are in the alpha stage, but we can pre-release them as they do not depend on Bootstrap v4 or v5 (other than some minimal CSS styling)

Icons are not automatically installed!

Users have the option of importing the IconsPlugin (or BootstrapVueIcons) to install all icons, or they can import individual icon components (BIcon{Name}) as needed.

Added option icons to Nuxt module to include BootstrapVueIcons when true

To Do:

• Create a build script to generate the icon components from bootstrap-icons/icons/*.svg
• add props for basic transforms such as rotate, flip, and shift, mimicking features available in FontAwesome
• update Nuxt module docs re icons plugin
• name-space all icon SCSS with class .b-icon
• create an icon's only CSS file in dist
• create icons only dist bundles
• document icons only builds

Related;

• Icon vertical alignment and size issues twbs/icons#82 (alignment issues)
• [bug] skip-* icon names/svgs are mixed up, and also have hardcoded stroke color of black twbs/icons#84 (skip-* icon names are mixed up)

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)