feat: add option for view to follow cursor (#1727)

* feat: add option for custom entry view to follow cursor

Creates an option to allow the custom entries
view to follow the user's cursor as they type.

To enable, set
```lua
require("cmp").setup({
  view = {
    entries = {
      follow_cursor = true
    }
  }
})
```

Original source at 7569056388

Closes #1660

Co-authored-by: lvimuser <109605931+lvimuser@users.noreply.github.com>

* doc: add view.follow_cursor option to docs

---------

Co-authored-by: lvimuser <109605931+lvimuser@users.noreply.github.com>

doc/cmp.txt

@@ -686,6 +686,13 @@ view.docs.auto_open~
 
   Specify whether to show the docs_view when selecting an item.
 
+                                                 *cmp-config.view.follow_cursor*
+view.follow_cursor*
+  `boolean`
+
+  Specify whether the pmenu should follow the current position of the cursor
+  as the user types. `false` by default.
+
                            *cmp-config.window.{completion,documentation}.border*
 window.{completion,documentation}.border~
   `string | string[] | nil`