mempool: export checkStandardness func

[ellemouton]

Export checkStandardness func so that it can be used elsewhere

[coveralls]

Pull Request Test Coverage Report for Build 2148913830

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 54.135%

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Files with Coverage Reduction	New Missed Lines	%
txscript/taproot.go	2	95.93%

Totals
Change from base Build 2148764512:	0.004%
Covered Lines:	24800
Relevant Lines:	45811

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💛 - Coveralls

[Roasbeef]

LGTM 🍁

It might also be useful to eventually export some more mempool components as well? So enough to be able to give it a mock UTXO set and apply the normal contextual validation. This might already be possible however. I think maybe we should defer merging this till the lnd PR using the new functionality gets further along so we can consider everything as a whole? No strong feelings in this direction fwiw.

[ellemouton]

I think maybe we should defer merging this till the lnd PR using the new functionality gets further along so we can consider everything as a whole?

yeah agreed. Just wanted to open this one up so long so that the go.mod in the LND pr is pointing to something visable

[Roasbeef]

We're seeing more instances of this in lnd when users end up creating mega transactions, so I think it's worth landing this, then circling back to see if we can add more contextual validation.

[jcvernaleo]

OK