vim: add minimal ctrl+t/ctrl+d in insert mode

This isn't perfect, because we don't place the cursor on the exact
location due to how cursor saving is done. We might be able to fix that
by using a new mark, but we need to see if that messes anything else up
in the process.

Fixes #1019

src/plugins/vim/keybindings/vim.css

@@ -2112,6 +2112,21 @@
   bind "<ctrl>w" { "movement" (previous-word-start, 1, 1, 0)
                    "delete-selection" () };
 
+  bind "<ctrl>d" { "save-insert-mark" ()
+                   "movement" (first-nonspace-char, 0, 1, 0)
+                   "movement" (line-end, 1, 1, 0)
+                   "begin-user-action" ()
+                   "indent-selection" (-1)
+                   "end-user-action" ()
+                   "restore-insert-mark" () };
+  bind "<ctrl>t" { "save-insert-mark" ()
+                   "movement" (first-nonspace-char, 0, 1, 0)
+                   "movement" (line-end, 1, 1, 0)
+                   "begin-user-action" ()
+                   "indent-selection" (1)
+                   "end-user-action" ()
+                   "restore-insert-mark" () };
+
   bind "<ctrl>e" { "movement" (screen-up, 0, 0, 1) };
   bind "<ctrl>y" { "movement" (screen-down, 0, 0, 1) };