CheckTransaction (N.f.B: CheckCoinbase, CheckTransactionCommon and CheckRegularTransaction
in our case ) is a context-free function that does not require access to the blockchain
or mempool. Move it from src/consensus/tx_verify in lib_server to a new unit
src/consensus/tx_check in lib_consensus so that it can be called by non-server libraries.
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This is a partial backport of Core PR15638