vim: Fix relative motions (#2888)

This changes vim motions to be relative to fold lines, not display
lines, to match the behaviour of vim.

This is necessary for relative line numbers to make sense (as the most
important thing is you can do `3j` to get th e line that is numbered 3).


Release Notes:

- vim: Fix handling of motions when `soft_wrap` is enabled in zed. Like
in vim `j,k,up,down,$,^,0,home,end` will all now navigate in file
coordinates not display coordinates.
- vim: Add `g {j,k,up,down,$,^,0,home,end}` to navigate in display
coordinates.
- vim: Add `z o` and `z c` to open and close folds.
- vim: Add `z f` in visual mode to fold selection.

Note: this may be a jarring change if you're grown used to the current
behaviour of `j` and `k`. You can make the issue less acute by setting
`"soft_wrap":"none"` in your settings; or you can manually copy the
bindings for `g j` to the binding for `j` (etc.) in your keymap.json to
preserve the existing behaviour.

assets/keymaps/vim.json

@@ -137,10 +137,67 @@
           "partialWord": true
         }
       ],
+      "g j": [
+        "vim::Down",
+        {
+          "displayLines": true
+        }
+      ],
+      "g down": [
+        "vim::Down",
+        {
+          "displayLines": true
+        }
+      ],
+      "g k": [
+        "vim::Up",
+        {
+          "displayLines": true
+        }
+      ],
+      "g up": [
+        "vim::Up",
+        {
+          "displayLines": true
+        }
+      ],
+      "g $": [
+        "vim::EndOfLine",
+        {
+          "displayLines": true
+        }
+      ],
+      "g end": [
+        "vim::EndOfLine",
+        {
+          "displayLines": true
+        }
+      ],
+      "g 0": [
+        "vim::StartOfLine",
+        {
+          "displayLines": true
+        }
+      ],
+      "g home": [
+        "vim::StartOfLine",
+        {
+          "displayLines": true
+        }
+      ],
+      "g ^": [
+        "vim::FirstNonWhitespace",
+        {
+          "displayLines": true
+        }
+      ],
       // z commands
       "z t": "editor::ScrollCursorTop",
       "z z": "editor::ScrollCursorCenter",
       "z b": "editor::ScrollCursorBottom",
+      "z c": "editor::Fold",
+      "z o": "editor::UnfoldLines",
+      "z f": "editor::FoldSelectedRanges",
       // Count support
       "1": [
         "vim::Number",