perf(b-table, b-table-lite): improve render performance (closes #4211, #4155)

[tmorehouse]

Describe the PR

Improve performance of <b-table> and <b-table lite> by using native td/th in table <tbody> if the cell is not a sticky column (otherwise use a b-th/b-td where the instance intelligence is needed to handle cell variants for sticky columns)

This can dramatically reduce the number of Vue instances instantiated for extremely large tables (where overall cell counts are in the 1000's)

Closes #4211
Closes #4155
Might address #4150

Side note: if bootstrap v5 incorporates the proposed cell background inheritance, then our child helper components can be converted to functional components (which will further improve performance and remove the need for injection resolution)

PR checklist

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

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

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, fix typos, chore: 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
• 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)

[codecov]

Codecov Report

Merging #4213 into dev will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev    #4213      +/-   ##
==========================================
+ Coverage   99.86%   99.86%   +<.01%     
==========================================
  Files         237      237              
  Lines        4525     4534       +9     
  Branches     1274     1280       +6     
==========================================
+ Hits         4519     4528       +9     
  Misses          5        5              
  Partials        1        1

Impacted Files	Coverage Δ
src/components/table/helpers/mixin-tbody-row.js	100% <100%> (ø)	⬆️

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