Make editor dimming a core workbench feature

[Tyriar]

The dim unfocused feature is currently built using some CSS overrides to accomplish the majority of what users wanted without much work. For example:

vscode/src/vs/workbench/contrib/accessibility/browser/unfocusedViewDimmingContribution.ts

Lines 38 to 62 in 35be9bf

	if (opacity !== 1) {
	// These filter rules are more specific than may be expected as the `filter`
	// rule can cause problems if it's used inside the element like on editor hovers
	const rules = new Set<string>();
	const filterRule = `filter: opacity(${opacity});`;
	// Terminal tabs
	rules.add(`.monaco-workbench .pane-body.integrated-terminal:not(:focus-within) .tabs-container { ${filterRule} }`);
	// Terminals
	rules.add(`.monaco-workbench .pane-body.integrated-terminal .terminal-wrapper:not(:focus-within) { ${filterRule} }`);
	// Text editors
	rules.add(`.monaco-workbench .editor-group-container:not(.active) .monaco-editor { ${filterRule} }`);
	// Breadcrumbs
	rules.add(`.monaco-workbench .editor-group-container:not(.active) .tabs-breadcrumbs { ${filterRule} }`);
	// Terminal editors
	rules.add(`.monaco-workbench .editor-group-container:not(.active) .terminal-wrapper { ${filterRule} }`);
	// Settings editor
	rules.add(`.monaco-workbench .editor-group-container:not(.active) .settings-editor { ${filterRule} }`);
	// Keybindings editor
	rules.add(`.monaco-workbench .editor-group-container:not(.active) .keybindings-editor { ${filterRule} }`);
	// Editor placeholder (error case)
	rules.add(`.monaco-workbench .editor-group-container:not(.active) .monaco-editor-pane-placeholder { ${filterRule} }`);
	// Welcome editor
	rules.add(`.monaco-workbench .editor-group-container:not(.active) .gettingStartedContainer { ${filterRule} }`);
	cssTextContent = [...rules].join('\n');
	}

Since this relies upon internal CSS classes it's prone to break though. When this feature went through the test phase there were a collection of problems reported, mostly around certain edge cases not working. I'm merging all those issues into this one to track any further development on the feature if we choose to do so:

• editor should not be dimmed when navigating search results #190102
• Unclear what part of the editor is dimmed #191608
• Notebooks are not dimming #191615
• Support unfocused dimming of all workbench components like output and debug console #191616
• Unfocused editors should regain focus (be un-dimmed) on scroll #191671
• Does not regain focus on minimap #191714
• Workspace trust editor is not dimmed #191743
• Running extensions editor is not dimmed #191744
• Editor dimming should be a core workbench feature #191757
• Polish unfocused dimming feature #191775