Updates the RunInactivityChecks() function:
- rename to ShouldRunInactivityChecks (https://github.com/bitcoin/bitcoin/pull/20721#discussion_r576394790)
- take optional time now (https://github.com/bitcoin/bitcoin/pull/20721#discussion_r575895661)
- call from within InactivityChecks (https://github.com/bitcoin/bitcoin/pull/20721#discussion_r575894665)
- update comment (https://github.com/bitcoin/bitcoin/pull/20721#discussion_r575894343)
- change ordering of inequality (https://github.com/bitcoin/bitcoin/pull/20721#discussion_r574925129)
- ~make inline (https://github.com/bitcoin/bitcoin/pull/20721#discussion_r574903578)~