gcs+gcs/builder: update BIP 158 generation code to match latest BIP changes

[Roasbeef]

In this PR, we update the BIP 158 generation code to match the latest BIP changes. The notable changes are:

• regular filter no longer includes the txid
• we now use distinct M and N values rather than setting P as it results in a small improvement
• the regular filter now uses the prev output scripts rather than the outpoint as it achieves better compression
• there's no longer an extended filter
• when indexing scripts, we skip all OP_RETURN outputs

[aakselrod]

utACK.