search menu tests for 2.9/edit-search-regressions

it's mainly to test "Edit Search" in #page-navigation of pages like Merge,
Link/FromIncident, Link/ToIncident, Incident "Reply to Reporters" and "Reply
to All".
Merge branch '3.0/search-menu-tests' into 3.0.0-releng
Reduce our extra Query Args when pulling from the session.

As discovered by sunnavy when he went spelunking to determine why
t/walk-web.t started running so many extra tests (7a630ac1), we were
stuffing a bunch of extra query params into the query string,
depending on whether we did that from the hash or passed args (things
like Object and Description).

I rewrote his patch a bit to use the same Field list as search_arguments

We lose saved search state badly in RTIR, but it's not a regression
caused by this code, see [rtir #25241]
Better explain the actual behavior of this option.

When introduced in 591dfd0, this option limited the
Transactions/Attachments we were going to FTS on, which makes sense.

For performance reasons, it was removed from the Custom Field searches
prior to 2.4.4 in 8807723.  However, that commit didn't fix the docs,
and it didn't consider that Lookups now act weirdly based on what you're
searching for.

In [rtir #14427] I lay out the history and possible fixes.  For 3.0.0,
documentation is the best solution.