Metadata: Retain a subset of metadata pallets

[lexnv]

This PR strips the metadata to include only some provided pallets.

Metadata size with single pallet

The No Generics means that the extrinsic types were stripped of the generic type parameters.
Those generics where not needed and include nested type IDs that are unnecessarily increasing
the final metadata size. (Relies on paritytech/scale-info#176).

No Generics	With Generics	Pallet
244K	244K	Alliance.scale
240K	240K	AllianceMotion.scale
8,0K	240K	AssetTxPayment.scale
32K	244K	Assets.scale
12K	12K	Auctions.scale
8,0K	240K	AuthorityDiscovery.scale
8,0K	240K	Authorship.scale
16K	244K	Babe.scale
16K	244K	Balances.scale
16K	244K	Bounties.scale
16K	240K	ChildBounties.scale
12K	12K	Claims.scale
16K	16K	Configuration.scale
28K	252K	Contracts.scale
16K	240K	ConvictionVoting.scale
16K	240K	CoreFellowship.scale
240K	240K	Council.scale
16K	16K	Crowdloan.scale
248K	248K	Democracy.scale
8,0K	8,0K	Dmp.scale
20K	248K	ElectionProviderMultiPhase.scale
16K	244K	Elections.scale
12K	240K	FastUnstake.scale
8,0K	240K	Glutton.scale
12K	240K	Grandpa.scale
8,0K	240K	Historical.scale
16K	16K	Hrmp.scale
20K	244K	Identity.scale
12K	240K	ImOnline.scale
12K	240K	Indices.scale
8,0K	8,0K	Initializer.scale
240K	240K	Lottery.scale
12K	240K	MessageQueue.scale
8,0K	240K	Mmr.scale
240K	240K	Multisig.scale
44K	252K	Nfts.scale
20K	248K	Nis.scale
28K	248K	NominationPools.scale
8,0K	240K	Offences.scale
12K	12K	ParaInclusion.scale
12K	12K	ParaInherent.scale
12K	12K	ParaScheduler.scale
8,0K	8,0K	ParaSessionInfo.scale
8,0K	8,0K	ParachainsOrigin.scale
20K	20K	Paras.scale
12K	12K	ParasDisputes.scale
8,0K	8,0K	ParasShared.scale
16K	16K	PhragmenElection.scale
8,0K	240K	Pov.scale
12K	240K	Preimage.scale
240K	240K	Proxy.scale
8,0K	240K	RandomnessCollectiveFlip.scale
12K	240K	RankedCollective.scale
248K	248K	RankedPolls.scale
244K	244K	Recovery.scale
248K	248K	Referenda.scale
12K	12K	Registrar.scale
8,0K	240K	Remark.scale
8,0K	240K	RootTesting.scale
12K	240K	Salary.scale
240K	240K	Scheduler.scale
12K	240K	Session.scale
12K	12K	Slots.scale
20K	244K	Society.scale
36K	252K	Staking.scale
12K	240K	StateTrieMigration.scale
240K	240K	Sudo.scale
312K	312K	System.scale
240K	240K	TechnicalCommittee.scale
12K	240K	TechnicalMembership.scale
8,0K	240K	Timestamp.scale
16K	240K	Tips.scale
8,0K	240K	TransactionPayment.scale
12K	240K	TransactionStorage.scale
12K	240K	Treasury.scale
12K	12K	Ump.scale
28K	244K	Uniques.scale
240K	240K	Utility.scale
12K	240K	Vesting.scale
12K	244K	VoterList.scale
240K	240K	Whitelist.scale
36K	36K	XcmPallet.scale
468K	468K	polkadot_metadata.scale

Closes #629.

// CC @paritytech/subxt-team

[jsdw]

Awesome; looks like removing those generic types had a really notable impact! (allets like Sudo and MultiSig I guess depend on RuntimeCall for the inner stuff which depends on types from all other pallets, so it makes sense that they are still big :))

[jsdw]

Looks great; happy to see this merge :)

[jsdw]

Instead of trying to strip type params out of the extrinsic type (whose effect is primarily to remove the reference to the RuntimeCall type), I now strip the RuntimeCall type variants to only include those for pallets we want to keep. This keeps the size fairly uniformly small across all pallets now (below based on artifacts/polkadot.metadata):

pallet	size
System	64233
Scheduler	13027
Preimage	9102
Babe	14074
Timestamp	7879
Indices	10815
Balances	14605
TransactionPayment	8060
Authorship	8461
Staking	35015
Offences	7783
Historical	6555
Session	10574
Grandpa	11876
ImOnline	10598
AuthorityDiscovery	6563
Democracy	23583
Council	16705
TechnicalCommittee	16749
PhragmenElection	15828
TechnicalMembership	8984
Treasury	11710
Claims	11536
Vesting	11809
Utility	13546
Identity	21004
Proxy	16162
Multisig	16092
Bounties	13829
ChildBounties	14950
Tips	13978
ElectionProviderMultiPhase	18513
VoterList	12627
NominationPools	23233
FastUnstake	10442
ParachainsOrigin	6561
Configuration	14857
ParasShared	7399
ParaInclusion	12255
ParaInherent	11830
ParaScheduler	9923
Paras	17175
Initializer	8226
Dmp	7453
Ump	11275
Hrmp	15863
ParaSessionInfo	8246
ParasDisputes	9899
Registrar	12484
Slots	9715
Auctions	11495
Crowdloan	14214
XcmPallet	36657