show_blocking_widget debug option makes the application hang

[YgorSouza]

Describe the bug

Enabling the show_blocking_widget option causes the application to hang. Observed both locally and on https://www.egui.rs/

To Reproduce
Steps to reproduce the behavior:

1. Go to https://www.egui.rs/
2. Open Settings windows and expand the Debug collapsing header
3. Check the last option "Show what widget blocks the interaction of another widget"
4. The UI stops responding, without using any CPU

Expected behavior

The debug option draws the overlapping rectangles and doesn't freeze the UI.

Screenshots

Desktop (please complete the following information):

• OS: Fedora 37
• Browser Firefox
• Version 110.0

Additional context

This is the code that runs when this option is enabled:

egui/crates/egui/src/context.rs

Lines 587 to 598 in 7215fdf

	if ctx.memory.options.style.debug.show_blocking_widget {
	Self::layer_painter(self, LayerId::debug()).debug_rect(
	interact_rect,
	Color32::GREEN,
	"Covered",
	);
	Self::layer_painter(self, LayerId::debug()).debug_rect(
	prev_rect,
	Color32::LIGHT_BLUE,
	"On top",
	);
	}

The problem seems to be that this code being called inside a Context::write() call, whereas both acquiring and using the layer painter requires some Context::read() and Context::write() calls, so it causes a deadlock.

[crumblingstatue]

I can reproduce it in the web version on chromium 110, Linux