When a copmonent directory is set to the front page, don't interfere with blog searches.
WP's default search query arg is 's', so that URLs like example.com?s=foo lead
to a search of blog posts on the term 'foo'. When a BuddyPress component page
like Members is set to the front page, it interferes with this behavior in two
ways: (1) BuddyPress interprets example.com?s=foo as a Members directory
request, and (2) the 's' query arg is interpreted as a Members search term.
We fix this conflict as follows:
- During the URL parsing process, don't interpret requests of the form example.com?s=foo as being BP component requests, even if a BP component is set to the front page.
- In order to make BuddyPress component searches continue to work, we change the default search query arguments for each component to be unique. For example, member directory searches look like example.com?members_search=foo. Components register their own 'search_query_arg', and these args can be filtered with the new 'bp_core_get_component_search_query_arg' filter.
Fixes #5087.