support prompt history in isearch

previously, exiting the isearch prompt would `_cancel` which discards
prompt contents. swapping this for `_submit` causes prompt history to
be saved similar to other prompts.

since `up` and `down` already control moving between matches, use
`C-n` and `C-p` (similar to readline) for navigating prompt history.

editor.c

@@ -1984,11 +1984,13 @@ static void _editor_init_kmaps(editor_t *editor) {
         MLE_KBINDING_DEF("_editor_prompt_isearch_viewport_up", "pgup"),
         MLE_KBINDING_DEF("_editor_prompt_isearch_viewport_down", "pgdn"),
         MLE_KBINDING_DEF("_editor_prompt_isearch_drop_cursors", "C-/"),
-        MLE_KBINDING_DEF("_editor_prompt_cancel", "enter"),
-        MLE_KBINDING_DEF("_editor_prompt_cancel", "M-enter"),
-        MLE_KBINDING_DEF("_editor_prompt_cancel", "C-c"),
-        MLE_KBINDING_DEF("_editor_prompt_cancel", "C-x"),
-        MLE_KBINDING_DEF("_editor_prompt_cancel", "M-c"),
+        MLE_KBINDING_DEF("_editor_prompt_input_submit", "enter"),
+        MLE_KBINDING_DEF("_editor_prompt_input_submit", "M-enter"),
+        MLE_KBINDING_DEF("_editor_prompt_input_submit", "C-c"),
+        MLE_KBINDING_DEF("_editor_prompt_input_submit", "C-x"),
+        MLE_KBINDING_DEF("_editor_prompt_input_submit", "M-c"),
+        MLE_KBINDING_DEF("_editor_prompt_history_up", "C-p"),
+        MLE_KBINDING_DEF("_editor_prompt_history_down", "C-n"),
         MLE_KBINDING_DEF(NULL, NULL)
     });
 }

tests/func/test_search_replace.sh

@@ -56,13 +56,20 @@ expected[rfind_cursor_line]='^bview.0.cursor.0.mark.line_index=1$'
 expected[rfind_cursor_col ]='^bview.0.cursor.0.mark.col=0$'
 source 'test.sh'
 
-# cmd_isearch
+# cmd_isearch 1
 macro='a c t o r enter a p p l e enter a p p e t i t e enter a z u r e M-\ C-r a p p e enter'
 declare -A expected
 expected[isearch_cursor_line]='^bview.0.cursor.0.mark.line_index=2$'
 expected[iesarch_cursor_col ]='^bview.0.cursor.0.mark.col=0$'
 source 'test.sh'
 
+# cmd_isearch 2
+macro='i enter a enter b enter a enter b M-\ C-r a enter C-r b enter C-r C-n C-n'
+declare -A expected
+expected[isearch_cursor_line]='^bview.0.cursor.0.mark.line_index=3$'
+expected[iesarch_cursor_col ]='^bview.0.cursor.0.mark.col=0$'
+source 'test.sh'
+
 # cmd_replace 1
 macro='a 1 space b 2 space c 3 space d 4 C-t \ d + enter x enter y n a'
 declare -A expected