Internalize BevyManifest logic. Switch to RwLock #59388

Job	Run time
miri	15m 57s
ci	4m 50s
build (windows-latest)	14m 6s
build (ubuntu-latest)	8m 27s
check-bevy-internal-imports	11s
check-doc	11m 47s
build (macos-latest)	10m 23s
check-missing-examples-in-docs	30s
toml	1m 52s
typos	8s
check-missing-features-in-docs	26s
markdownlint	1m 10s
check-compiles-no-std-portable-atomic	56s
check-compiles-no-std	1m 4s
check-compiles	7m 43s
build-wasm-atomics	1m 54s
build-wasm	1m 26s
msrv	1m 42s
	1h 24m 32s

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