Rename PluginGroupBuilder: add -> push, add_group -> push_group #48422

Job	Run time
ci	2m 8s
miri	10m 19s
check-doc	9m 11s
build (windows-latest)	6m 56s
toml	1m 53s
build (ubuntu-latest)	2m 37s
run-examples-macos-metal	4m 46s
typos	7s
build (macos-latest)	2m 48s
check-bevy-internal-imports	4s
check-missing-examples-in-docs	29s
check-missing-features-in-docs	40s
markdownlint	1m 13s
check-compiles	0s
build-wasm-atomics	1m 31s
build-wasm	42s
msrv	1m 5s
	46m 29s

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