Slow decompiler highlighting

[sad-dev]

Describe the bug
When the existing number of highlighters that apply to a function is large (global highlighters + secondary for that function), the computation of token highlights is extremely slow. This is made worse by #3749 which prevents a user from creating a secondary highlight, meaning all highlights are global and will apply to all functions.

The responsible code path for global highlights is as follows (there is a similar path for secondary highlights)
Note the multiple iterations over highlighters (as well as double call to clearHighlights) which causes unnecessary quadratic complexity in computation.
There may also be other similar issues in the code for clearing highlights

DecompilerPanel.reapplyGlobalHighlights
		Set<DecompilerHighlighter> globalHighlighters = highlightController.getGlobalHighlighters();
		for (DecompilerHighlighter highlighter : globalHighlighters) {
			highlighter.clearHighlights();
			highlighter.applyHighlights();
		}
ClangDecompilerHighlighter.applyHighlights
		clearHighlights();
		Map<ClangToken, Color> highlights = new HashMap<>();
		try {
			matcher.start(root);
			gatherHighlights(root, highlights);
		}
		finally {
			matcher.end();
		}
		Supplier<? extends Collection<ClangToken>> tokens = () -> highlights.keySet();
		ColorProvider colorProvider = new MappedTokenColorProvider(highlights);
		decompilerPanel.addHighlighterHighlights(this, tokens, colorProvider);
DecompilerPanel.addHighlighterHighlights
ClangHighlightController.addHighlighterHighlights
ClangHighlightController.addTokensToHighlights
		for (ClangToken clangToken : tokens) {
			Color color = colorProvider.getColor(clangToken);
			doAddHighlight(clangToken, color, currentHighlights);
		}
ClangHighlightController.doAddHighlight
ClangHighlightController.updateHighlightColor
ClangHighlightController.getCombinedColor
ClangHighlightController.blendHighlighterColors
		Set<DecompilerHighlighter> global = getGlobalHighlighters();
		Set<DecompilerHighlighter> secondary = getSecondaryHighlighters(function);
		Iterable<DecompilerHighlighter> it = CollectionUtils.asIterable(global, secondary);
		Color lastColor = null;
		for (DecompilerHighlighter highlighter : it) {
		        ...
                }

[dragonmacher]

How many highlighters does it take for you to notice this behavior?

[sad-dev]

Roughly 30 highlighters that apply to a function with hundreds of highlighted tokens is enough to impose noticeable (>30s) delays