Fixes #24811 (closed).
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