Refactor Project API to reflect changes upstream

projectile-project-root no longer returns `default-directory` if not in
a project (it returns nil). As such, doom-project-* functions (and their
uses) have been refactored.

+ doom-project-p & doom-project-root are aliases for
  projectile-project-p & projectile-project-root.
+ doom-project-{p,root,name,expand} now has a DIR argument (for
  consistency, since projectile-project-name and
  projectile-project-expand do not).
+ The nocache parameter is no longer necessary, as projectile's caching
  behavior is now more sane.
+ Removed some projectile advice/hacks that are no longer necessary.
+ Updated unit tests

modules/ui/modeline/config.el

@@ -314,7 +314,7 @@ e.g. ~/w/project/src/lib/file.c
 Meant for `+modeline-buffer-path-function'."
   (pcase-let
       ((`(,root-parent ,root ,dir, file)
-        (shrink-path-file-mixed (doom-project-root)
+        (shrink-path-file-mixed (or (doom-project-root) default-directory)
                                 (file-name-directory buffer-file-name)
                                 buffer-file-name)))
     (list (cons root-parent 'font-lock-comment-face)