feat: add lazyPlugins() helper for conditional plugin loading #4910

Job	Run time
detect-changes	8s
download-previous-rolldown-binaries	13s
Build vite-plus packages (ubuntu-latest)	7m 25s
Build vite-plus packages (windows-latest)	13m 6s
${{ matrix.project.name }} E2E test (${{ matrix.os }})	1s
Notify on failure	1s
	20m 54s

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