feat(cursor): use cursor-shape-v1 cursor names instead of Gdk::CursorType

[J0hannes101]

Replace Gdk::CursorType enum values used for setting cursors with CSS cursor name strings (e.g. "default", "grab").

Background:

• in !8247 support for the cursor_shape_v1 protocol was backported to gtk3
• a cursor is set using a Gdk::CursorType enum value, GTK does not map that value to the corresponding cursor_shape_v1 cursor name
• As a result, GTK falls back to its own cursor theme instead of using the cursor provided by the compositor through cursor_shape_v1

Breaking changes:

• "cursor" now accepts a CSS cursor name string:

"custom/my-custom-module": {
    ...
    "cursor": "grab",
}

• Integer values (e.g. "cursor": 8) are no longer supported