Experimental: Update Boost to use new WordPress UI components

[rcoll]

Fixes #

Proposed changes

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 5 files.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/boost/app/assets/src/js/features/ui/pill/pill.tsx	0/3 (0.00%)	0.00%	1 ❤️‍🩹
projects/plugins/boost/app/assets/src/js/features/cornerstone-pages/prerender/prerender.tsx	0/17 (0.00%)	0.00%	-1 💚
projects/plugins/boost/app/assets/src/js/features/page-cache/meta/meta.tsx	0/69 (0.00%)	0.00%	-1 💚
projects/plugins/boost/app/assets/src/js/features/ui/collapsible-meta/collapsible-meta.tsx	0/8 (0.00%)	0.00%	-2 💚
projects/plugins/boost/app/assets/src/js/features/ui/close-button/close-button.tsx	0/2 (0.00%)	0.00%	-3 💚

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