Vector has a wgVectorResponsive flag. This adds a ResourceLoader
module as well
I propose the configuration is repurposed to disable the min-width
on Vector and enable the viewport tag. This will allow us to use
test.wikipedia.org to test Vector at lower resolutions in future
as well as provide a suitable option for 3rd parties wanting to run
a responsive version of Vector that can be opted into using:
```
$wgVectorResponsive = true;
$wgVectorDefaultSkinVersion = '2';
```
As part of this change, the default skin version is set to 2, in
preparation for the next MediaWiki release. Note on Wikimedia wikis we
explicitly set this version so this will not impact any of our deployed
wikis.
Bug: T242772
Change-Id: I878920f49d18c5d60efd3ac45dc7912d2c62086e
68b989efb6