Support completion boundaries when completing olp, tags, and agenda filter

* lisp/org-agenda.el (org-agenda-filter-completion-function):
* lisp/org-refile.el (org-olpath-completing-read):
* lisp/org-tags.el (org-tags-completion-function): Add support for
orderless/flex completion styles that require boundaries operation.

lisp/org-agenda.el

@@ -8194,10 +8194,12 @@ which see."
 	(confirm (lambda (x) (stringp x)))
 	(prefix "")
 	(operator "")
-	table)
+	table
+        begin)
     (when (string-match "^\\(.*\\([-+<>=]\\)\\)\\([^-+<>=]*\\)$" string)
       (setq prefix (match-string 1 string)
 	    operator (match-string 2 string)
+            begin (match-beginning 3)
 	    string (match-string 3 string)))
     (cond
      ((member operator '("+" "-" "" nil))
@@ -8214,6 +8216,11 @@ which see."
     (pcase flag
       (`t (all-completions string table confirm))
       (`lambda (assoc string table)) ;exact match?
+      (`(boundaries . ,suffix)
+       (let ((end (if (string-match "[-+<>=]" suffix)
+                      (match-string 0 suffix)
+                    (length suffix))))
+         `(boundaries ,(or begin 0) . ,end)))
       (`nil
        (pcase (try-completion string table confirm)
 	 ((and completion (pred stringp))

lisp/org-refile.el

@@ -775,6 +775,14 @@ this function appends the default value from
 				 (concat string (substring r 0 (match-end 0)) f)
 			       x)))
 			 (all-completions string thetable predicate))))
+              ((eq (car-safe action) 'boundaries)
+               ;; See `completion-file-name-table'.
+               (let ((start (or (and (string-match "/" string)
+                                     (match-beginning 0 string))
+                                (length string)))
+                     (end (and (string-match "/" (cdr action))
+                               (match-beginning 0 (cdr action)))))
+                 `(boundaries ,start . ,end)))
 	      ;; Exact match?
 	      ((eq flag 'lambda) (assoc string thetable))))
 	   args)))

lisp/org.el

@@ -12020,13 +12020,20 @@ function is passed as a collection function to `completing-read',
 which see."
   (let ((completion-ignore-case nil)	;tags are case-sensitive
 	(confirm (lambda (x) (stringp (car x))))
-	(prefix ""))
+	(prefix "")
+        begin)
     (when (string-match "^\\(.*[-+:&,|]\\)\\([^-+:&,|]*\\)$" string)
       (setq prefix (match-string 1 string))
+      (setq begin (match-beginning 2))
       (setq string (match-string 2 string)))
     (pcase flag
       (`t (all-completions string org-last-tags-completion-table confirm))
       (`lambda (assoc string org-last-tags-completion-table)) ;exact match?
+      (`(boundaries . ,suffix)
+       (let ((end (if (string-match "[-+:&,|]" suffix)
+                      (match-string 0 suffix)
+                    (length suffix))))
+         `(boundaries ,(or begin 0) . ,end)))
       (`nil
        (pcase (try-completion string org-last-tags-completion-table confirm)
 	 ((and completion (pred stringp))