Move is_data_available check to fork-choice on_block

[hwwhww]

Address #3170

Note: need to check again the confidence level of this change.

[djrtwo]

I left some relatively minor comments on file/definition organization

Also, the fact that we have no tests change here is a bit unnerving -- seeming we don't have any tests for is_data_available() within fork-choice or state transition.

It might be good to upgtrade the fork-choice test format to include if a block is available. (and if not, be able to subsequently become available) but I'm not sure if we should do so here

[djrtwo]

excellent!

[hwwhww]

It might be good to upgtrade the fork-choice test format to include if a block is available. (and if not, be able to subsequently become available) but I'm not sure if we should do so here

We could do something like the way we hacked get_pow_block in on_merge_block tests:

consensus-specs/tests/core/pyspec/eth2spec/test/bellatrix/fork_choice/test_on_merge_block.py

Lines 29 to 50 in e9a7a6d

	def with_pow_block_patch(spec, blocks, func):
	def get_pow_block(hash: spec.Bytes32) -> spec.PowBlock:
	for block in blocks:
	if block.block_hash == hash:
	return block
	raise BlockNotFoundException()
	get_pow_block_backup = spec.get_pow_block
	spec.get_pow_block = get_pow_block
	class AtomicBoolean():
	value = False
	is_called = AtomicBoolean()
	def wrap(flag: AtomicBoolean):
	yield from func()
	flag.value = True
	try:
	yield from wrap(is_called)
	finally:
	spec.get_pow_block = get_pow_block_backup
	assert is_called.value

I'll open a ticket, but probably add it in the next next release?