core/types: support for optional blob sidecar in BlobTx

[fjl]

This PR removes the newly added txpool.Transaction wrapper type, and instead adds a way of keeping the blob sidecar within types.Transaction. It's better this way because most code in go-ethereum does not care about blob transactions, and probably never will. This will start mattering especially on the client side of RPC, where all APIs are based on types.Transaction. Users need to be able to use the same signing flows they already have.

However, since blobs are only allowed in some places but not others, we will now need to add checks to avoid
creating invalid blocks. I'm still trying to figure out the best place to do some of these. The way I have it currently is as follows:

• In block validation (import), txs are verified not to have a blob sidecar.
• In miner, we strip off the sidecar when committing the transaction into the block.
• In TxPool validation, txs must have a sidecar to be added into the blobpool.
  • Note there is a special case here: when transactions are re-added because of a chain reorg,
    we cannot use the transactions gathered from the old chain blocks as-is, because they will be missing
    their blobs. This was previously handled by storing the blobs into the 'blobpool limbo'. The code has now
    changed to store the full transaction in the limbo instead, but it might be confusing for code readers why
    we're not simply adding the types.Transaction we already have.

Code changes summary:

• txpool.Transaction removed and all uses replaced by types.Transaction again
• blobpool now stores types.Transaction instead of defining its own blobTx format for storage
• the blobpool limbo now stores types.Transaction instead of storing only the blobs
• checks to validate the presence/absence of the blob sidecar added in certain critical places

[karalabe]

I think the PR is overall good, the missing places for validation is

• Downloader, where blocks can arrive in pieces and we want to verify them without reconstructing the entire block first. Specifically, we should check after decoding the block bodies that there are no blob txs.
• When parsing blobs from JSON (i.e. RPC, remote client, etc), we should somehow add this check.
• When receiving transactions form the network, IMO we should also have a check there. This is a bit debatable because we have one in the txpool.

In general, I think the question is whether we want to validate the presence/absence of blocks at the usage sites or the entry sites. The PR tries to check for them when used, but it might be stricter if we validated them on entry point (rpc, network, etc). Or maybe I would do both, reject them on entry point as bad data and log.Error them later and reject them at usage points as programming error. That way we have a double check to make sure we didn't miss anything, but in theory should only ever hit it on bad user inpu.

[fjl]

I have added a check in InsertReceiptChain to cover fast sync. Regarding checks for transactions from JSON-RPC, it's not necessary because the validation in the txpool catches those. Trying to keep the checks minimal here...