Block: make blockchain mandatory in validation methods

[jochem-brouwer]

This PR:

• Makes blockchain parameter mandatory in validate methods of Block and BlockHeader
• Adds validateData method to Block
• Hoists the extraData check to the constructor of BlockHeader

Rationale:
If you called validate in BlockHeader without a blockchain, the only check which is being done is checking that extraData.length is within the current bounds of the maximum extraData. This can give consumers the false idea that the header is correct, but the method does practically nothing.

Validate is now explicitly used to validate against the parent BlockHeader (or Block). There is an additional function in Block which has the logic which does not need blockchain in case a consumer does have a block but no access to a blockchain. (We cannot do all this in the constructor of the Block, as we need access to Trie here which is async).

Note: hoisting the extraData check to the constructor makes the Ethash test fail, will open an issue for this, looks like this data is invalid (?). See #943

This mandatory blockchain parameter is necessary in #933, this PR simply ensures that we make this parameter mandatory so we can work on this uncle validation logic in the future.

[codecov]

Codecov Report

Merging #942 (6a21940) into master (84aaf81) will increase coverage by 0.72%.
The diff coverage is 22.22%.

Flag	Coverage Δ
block	76.36% <22.22%> (+1.65%)	⬆️
blockchain	78.04% <ø> (ø)
common	92.03% <ø> (ø)
ethash	82.08% <ø> (ø)
tx	88.54% <ø> (+0.17%)	⬆️
vm	87.21% <ø> (ø)

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[jochem-brouwer]

Rebased this one!

[ryanio]

this lgtm! nice idea for making the mock blockchain

[holgerd77]

Thanks, great! 👍