Closes #17214.

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This adjusts the load path for the ``configBridge.json`` file from one
that's relative to the user running the command (eg ``jekyll serve``),
to one that's relative to the ``source`` configuration setting for
Jekyll.

The result is that the user can now have a (customised) ``_config.yml``
for Jekyll anywhere on her filesystem and point to Bootstrap's
``docs`` directory to use as the ``source``.  Previously, in order to
customise it, the original ``_config.yml`` needed to be modified inside
(a forked) Bootstrap, and the ``jekyll`` command could only be run at
the root of the Bootstrap package as the original file path to
``configBridge.json`` was only valid there.

The existing behaviour is not affected.

Fixes #17196
Closes #17510

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Move them to footer, and remove duplicate ones.

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Fix #17173

Fix #17166

(reported by ianhernandez in Slack)

When a DOM node is passed to an HTML tooltip, the `title` node is only
moved if it is not already in the tooltip. Otherwise, `empty()` is used
instead of `detach()` before appending the `title` to avoid memory
leaks. If a DOM node is passed to a plain text tooltip, its text is
copied via jQuery `.text()`.

Replaces `.detach()` with `.empty()`, as `.detach()` is almost never
useful but instead leaks memory. The difference between `empty` and
`detach` is that the latter keeps all the attached jQuery events/data.
However, since we do not return the previous children, the user would
have to keep these themselves, thus they can `detach()` if necessary.

This is a port of https://github.com/twbs/bootstrap/pull/14552 to v4.

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Related to #17314.