Minor Tooling and UI Improvements (#1314)

* [wip]fix: disable fill and gradient tools on bmp images
- aims to fix #1161

* [wip]fix: disable gradient tool for bmp images

* fix: disable gradient tool for bitmap images
- fixes https://github.com/GraphiteEditor/Graphite/issues/1161

* [wip]fix: disable menu bar elements if no open document

* [WIP]feat: render certain menubar elements if document is open

* fix: conditional menu bar rendering fixes
- update menu bar on certain document actions
- fix menu bar order on rendering all elements

* refactor: change conditional menu elements property
- use existing 'disabled' property

* feat: render menu dropdown items conditionally

* fix: revert formatter whitespace changes

* refactor: improve variable naming and message usage
- name menu bar bool flag better
- use SendLayout message and remove unneeded calls

frontend/src/components/widgets/inputs/MenuBarInput.svelte

@@ -63,7 +63,7 @@
 				// New fields in `MenuListEntry`
 				shortcutRequiresLock: entry.shortcut ? shortcutRequiresLock(entry.shortcut.keys) : undefined,
 				value: undefined,
-				disabled: undefined,
+				disabled: entry.disabled ?? undefined,
 				font: undefined,
 				ref: undefined,
 			});