Eager expansion of the flycheck-define-checker macro causes flycheck to
be unavoidably eager-loaded at startup, regardless of other deferral
techniques, slowing down startup considerably, as it pulls in a number
of associated packages/config with it.
featurep! will be renamed modulep! in the future, so it's been
deprecated. They have identical interfaces, and can be replaced without
issue.
featurep! was never quite the right name for this macro. It implied that
it had some connection to featurep, which it doesn't (only that it was
similar in purpose; still, Doom modules are not features). To undo such
implications and be consistent with its namespace (and since we're
heading into a storm of breaking changes with the v3 release anyway),
now was the best opportunity to begin the transition.
Moved add-hook calls (for tree-sitter initialization) into their
respective modes' config blocks, or nearby, to be consistent with how
other, similar tools (like lsp!) are initialized, and does so at
runtime, rather than at expansion/compile time, which eval-when! caused.
