Remove `bevy_core` #54210

Job	Run time
build (windows-latest)	6m 26s
ci	2m 35s
miri	15m 20s
build (ubuntu-latest)	2m 56s
build (macos-latest)	2m 16s
check-bevy-internal-imports	6s
check-doc	9m 40s
check-missing-examples-in-docs	28s
run-examples-macos-metal	5m 7s
toml	1m 50s
typos	9s
check-missing-features-in-docs	27s
markdownlint	1m 2s
check-compiles-no-std	50s
check-compiles	4m 25s
msrv	1m 2s
build-wasm-atomics	1m 30s
build-wasm	43s
	56m 52s

Provide feedback