Will hopefully revert this reversion and land a fully-working version of UMD in v3.3.0.

Revert "some changes from #13801 - add strict mode back and =="
This reverts commit 2b302f69.

Revert "Fix regression of #10038 introduced by #13772"
This reverts commit e9d6756a.

Revert "MD/CommonJS/Globals #12909"
This reverts commit 1c6fa901.

Revert "address #13811"
This reverts commit f347d7d9.

Conflicts:
    js/carousel.js
    js/collapse.js
    js/dropdown.js
    js/modal.js
    js/tab.js
    js/tooltip.js

Closes #13782 by merging it.

fixes #13430

fix #13220 Scrollspy generates wrong offsets for a page-- recalculate offsets if `scrollheight` changes

faster and easier to test/develop js functionality not represented in unit tests, and gives us
a playground for interactions, etc.

It also makes it so developing javascript is now decoupled form jekyll, which should make everything
faster and less painful.

This commit also reverts my filter commit https://github.com/twbs/bootstrap/commit/9900771aa7f1b3ddcee49aec84082104776ace70
which broke scrollspy for dropdowns.

Closes #13702 by merging a rebased version of it.

`slideIndex` is assigned to the same value a few lines above.

Be more consistent across the whole codebase.

Also, make use of JSHint's 2.5.1 `extends` and `qunit` options. This way we set our basis options in js/.jshintrc and override the rest.

* register the callback before invoking the toggling
* listen for `hidden` instead of `hide`
* account for the possibility of the associated `show` event being preventDefault-ed

Adds relevant unit tests.

Generates a unique id for tooltip and adds [aria-describedby] to the element
it is called on. Resolves issue #13480

- set up test
- linted the code styles
- passed the tests
- integrated feedback from @cvrebert

primarily adds a data- attribute to the tooltip (and thus, the popover)
to create a self-reference.

Set top position to (scrollHeight - this.$element.height() - offsetBottom).