feat(corfu): more CAPFs and ergonomy changes

Add CAPFs from cape:
- `cape-dabbrev`;
- `cape-elisp-block`;
- `cape-file`;
Fix some CAPFs via cape:
- Make non-exclusive, purified and silent `pcomplete-completions-at-point`;
- Make non-exclusive and non-interruptable `lsp-completion-at-point`;
- Make non-exclusive `eglot-completion-at-point`;
- Make non-exclusive `comint-completion-at-point`;
Fix and improve keybindings:
- Smart `DEL`;
Add depth to CAPFs, allowing ordering to be adjustable.

modules/config/default/config.el

@@ -468,7 +468,13 @@ Continues comments if executed from a commented line. Consults
          [backtab] #'corfu-previous
          "TAB" #'corfu-next
          [tab] #'corfu-next))
-  (let ((cmds-ret
+  (let ((cmds-del
+         `(menu-item "Reset completion" corfu-reset
+           :filter ,(lambda (cmd)
+                      (when (and (>= corfu--index 0)
+                                 (eq corfu-preview-current 'insert))
+                        cmd))))
+         (cmds-ret
           `(menu-item "Insert completion DWIM" corfu-insert
              :filter ,(lambda (cmd)
                         (interactive)
@@ -488,6 +494,8 @@ Continues comments if executed from a commented line. Consults
                               (t cmd))))))
     (map! :when (modulep! :completion corfu)
           :map corfu-map
+          [backspace] cmds-del
+          "DEL" cmds-del
           :gi [return] cmds-ret
           :gi "RET" cmds-ret))