Docs/Examples/Manual: Keep focus when clear search input.

[abernier]

This was constantly annoying me, especially on mobile¹...

BEFORE: In the search field, when clearing my query (with the X button), I lost the focus and have to click on the field again (at 00:07 in the 1st screencast) to type another query

exitSearchButton.mp4

AFTER: I keep the focus and can continue typing a different query

clearSearchButton.mp4

NB: I've renamed (in a separate commit) the X button from exitSearchButton to clearSearchButton just to better reflect what it is now doing

Footnotes

1. especially on mobile because we cannot ctrl+a easily with the virtual keyboard. But tbh loosing focus was also annoying me on desktop if using the X button ↩

[Mugen87]

https://raw.githack.com/abernier/three.js/inputfilter-clear/docs/index.html

[Mugen87]

Normally I merge documentation related PRs but since this is a design/usability related issue, it's best if @mrdoob has a look at it first.

[mrdoob]

Looks good!