Update to 7.0.4xx nightlies, enable graph build, and signatures #1782

Job	Run time
Build on windows-latest for repo global.json	2m 46s
Build on windows-latest for 6.0 stable	3m 15s
Build on windows-latest for 7.0 preview	2m 43s
Build on macos-latest for repo global.json	2m 14s
Build on macos-latest for 6.0 stable	1m 32s
Build on macos-latest for 7.0 preview	1m 7s
Build on ubuntu-latest for repo global.json	56s
Build on ubuntu-latest for 6.0 stable	1m 16s
Build on ubuntu-latest for 7.0 preview	1m 0s
	16m 49s

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