add a layout debug mode that sets background colors #7335

Job	Run time
Pre-commit checks / Pre-commit Checks	46s
Check towncrier / Towncrier Checks	30s
Package Toga (android) / Create Python Package	22s
Package Toga (core) / Create Python Package	21s
Package Toga (cocoa) / Create Python Package	25s
Package Toga (demo) / Create Python Package	25s
Package Toga (dummy) / Create Python Package	16s
Package Toga (gtk) / Create Python Package	21s
Package Toga (iOS) / Create Python Package	16s
Package Toga (textual) / Create Python Package	15s
Package Toga (toga) / Create Python Package	18s
Package Toga (web) / Create Python Package	15s
Package Toga (winforms) / Create Python Package	27s
Test core (macos-latest, 3.9)	46s
Test core (macos-latest, 3.10)	56s
Test core (macos-latest, 3.11)	34s
Test core (macos-latest, 3.12)	35s
Test core (macos-latest, 3.13)	45s
Test core (ubuntu-latest, 3.9)	37s
Test core (ubuntu-latest, 3.10)	35s
Test core (ubuntu-latest, 3.11)	32s
Test core (ubuntu-latest, 3.12)	41s
Test core (ubuntu-latest, 3.13)	57s
Test core (windows-latest, 3.9)	50s
Test core (windows-latest, 3.10)	50s
Test core (windows-latest, 3.11)	50s
Test core (windows-latest, 3.12)	50s
Test core (windows-latest, 3.13)	41s
Testbed	1s
Coverage	1s
	15m 58s

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