Validation tooltip example

[mdo]

Fixes #24811.

This adds .valid-feedback to our custom styles and server side examples; previously we ommitted this to suggest you don't always need valid feedback. In addition, this adds examples of the .{valid|invalid}-tooltip classes with a new subsection in the Validation docs.

This also update the validation tooltip styles to remove the fixed width; instead it should retain itself to the parent element.

/cc @ysds @tmorehouse

[ysds]

Thanks. It is more helpful if documented that parent of .{valid|invalid}-tooltip needs to have position: relative like http://localhost:9001/docs/4.0/components/dropdowns/#examples

Wrap the dropdown’s toggle (your button or link) and the dropdown menu within .dropdown, or another element that declares position: relative;.

[mdo]

@ysds Added!