Migrate version switcher JS from the jinja templates

[damianavila]

On the version switcher PR that was recently merged I have requested some changes (
#436 (comment)) that we agreed it would be material for a follow-up PR.
This is an issue to capture that idea and link the implementation when that one is written.

[pradyunsg]

FWIW, this interfaces closely with pradyunsg/sphinx-basic-ng#12 (where I'm trying to figure out a way to have agnostic-to-hosting version and language switchers).

[damianavila]

Thanks for the reference, @pradyunsg.
I will take at it soon!!

[damianavila]

Related (since it involves moving JS from the templates into some other place): #28

[12rambau]

Isn't it the case ?

pydata-sphinx-theme/src/pydata_sphinx_theme/assets/scripts/index.js

Line 275 in adc8b1d

function checkPageExistsAndRedirect(event) {

[drammock]

Yes, this is done!