Flexbox grid column wrapping bug

Add nested definition list to docs example

Add comprehensive `.form-control` example(/testcase) to docs

Refs #18458
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[skip sauce]

Put all the textual input types right next to each other for easy visual comparison.
Refs #17308, #18763

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v4: Nav cleanup

- Moves styles up the document a bit to nest them
- Drops the static 1px for $navbar-tabs-border-width so once again it’s
all tied together should folks customize that

- Renames old and unused $nav-pills-active-link-hover-* for
$nav-pills-active-link-* ones
- Puts those vars to use in place of defaults $component-* vars on nav
pills

- Add new $nav-tabs-border-width for the bottom border on the .nav-tabs
parent class
- Use that new variable for the negative margin on nav-items within it
for consistent customization
- Drop the $nav-tabs-link-border-width for the new variable so it’s all
tied together

So folks can customize the distance between nav links in inline navs.

- More consistent states and labels in nav examples
- Add stacked pills example for with <nav> element

Refs #18708
[ci skip]

Add documentation for Tab plugin's `show` method

v4: Drop pager component

Erratum from #18778
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Erratum from #18658
[ci skip]

fixes #18658: no more min-width action on progress bars. we had them in v3 and ended up removing them for additional problems it caused folks.