Description of Pull Request:

Introduce a new pretranspile option for for users using nuxt module.

BootstrapVue ships with pre-transpiled es/ dist. This has many advantages and does not needs transpiling again. But as it has a wider babel config (for browser support) than Nuxt, transpiling on final project produces bundles with less size and better runtime perf in flavor of more compile time.

This option by default is only enabled for production mode so we have both speed and final build quality.

Results on a starter nuxt project with BV:

usePretranspiled: true: (es/)

• 906 KB
• 221 KB Gzip
• Build time: 20.51s

usePretranspiled: false: (src/)

• 829 KB
• 210KB Gzip
• Build time: 27.7s

Using src/ takes more 7.2 sec and reduces bundle size for 77 KB (11 KB Gzip)

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)