Tests

Implements support for external package loading in validator. #10575

Job	Run time
fixup / block-fixup	6s
labels / InternalPRRequired	1s
lint / bazel	2m 33s
test (linux, ubuntu-20.04) / bazel	2m 6s
test (linux, ubuntu-20.04, -debug) / bazel	4m 12s
test (linux, ubuntu-20.04, -asan) / bazel	2m 27s
test (macOS, macos-15) / bazel	3m 28s
test (windows, windows-2022) / bazel	16m 41s
	31m 34s

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