project-remember-project: Support calling it interactively

* lisp/progmodes/project.el (project-remember-project):
Support interactive invocation (bug#78099) and react with
appropriate messages when called so, depending on the blacklist.

etc/NEWS

@@ -429,6 +429,8 @@ This user option describes projects that should always be skipped by
 *** New command 'project-save-some-buffers' bound to 'C-x p C-x s'.
 This is like 'C-x s', but only for this project's buffers.
 
+*** 'project-remember-project' can now be called interactively.
+
 ** Registers
 
 *** New functions 'buffer-to-register' and 'file-to-register'.

lisp/progmodes/project.el

@@ -1936,12 +1936,18 @@ has changed, and NO-WRITE is nil."
 If project PR satisfies `project-list-exclude', then nothing is done.
 Save the result in `project-list-file' if the list of projects
 has changed, and NO-WRITE is nil."
-  (let ((root (project-root pr)))
-    (unless (seq-some (lambda (r)
-                        (if (functionp r)
-                            (funcall r pr)
-                          (string-match-p r root)))
-                      project-list-exclude)
+  (interactive (list (project-current t)))
+  (let ((root (project-root pr))
+        (interact (called-interactively-p 'any)))
+    (if (seq-some (lambda (r)
+                    (if (functionp r)
+                        (funcall r pr)
+                      (string-match-p r root)))
+                  project-list-exclude)
+        (when interact
+          (message "Current project is blacklisted!"))
+      (when interact
+        (message "Current project remembered"))
       (project--remember-dir root no-write))))
 
 (defun project--remove-from-project-list (project-root report-message)