ENH Make gridfield search options more accessible

[GuySartorelli]

Add some text to the "advanced" specific search filter dropdown button.
This applies both for searching for pages and searching in a gridfield.

This is following UX advice that came up during the development of silverstripe/silverstripe-framework#10382 - the intention being to make it clearer that there are additional search options (basically advanced search filters, usually, but theoretically these could be used to add arbitrary fields that can be used for arbitrary purposes in a custom SearchContext) available.

[emteknetnz]

@GuySartorelli could you rebase and rebuild bundle.js to resolve merge conflict please

[GuySartorelli]

Rebased.

[emteknetnz]

git diff found modified files when it should not have: D moment-locales/en-SG.js

This sounds familiar, look at the history of this file to see if you get any clues

May need to use git mv if it's a filename capitilisation issue

[GuySartorelli]

It was just a filename case sensitivity issue. The file content is already exactly the same in the lower-case version, so I've deleted the upper case version. Passing now.

Failing behat tests are unrelated - fixed in #1336

[emteknetnz]

Approved, tested locally

Before

After