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

editor/src/messages/layout/utility_types/widgets/menu_widgets.rs

@@ -37,12 +37,14 @@ pub struct MenuBarEntry {
 	pub shortcut: Option<ActionKeys>,
 	pub action: WidgetHolder,
 	pub children: MenuBarEntryChildren,
+	pub disabled: bool,
 }
 
 impl MenuBarEntry {
-	pub fn new_root(label: String, children: MenuBarEntryChildren) -> Self {
+	pub fn new_root(label: String, disabled: bool, children: MenuBarEntryChildren) -> Self {
 		Self {
 			label,
+			disabled,
 			children,
 			..Default::default()
 		}
@@ -67,6 +69,7 @@ impl Default for MenuBarEntry {
 			shortcut: None,
 			action: MenuBarEntry::no_action(),
 			children: MenuBarEntryChildren::empty(),
+			disabled: false,
 		}
 	}
 }