Upgrade priority: Low. Internal maintenance updates, focussed on internal optimizations.

Changelog:

• Optimize Extrinsic & block handling (Thanks to https://github.com/nazar-pc)
• Add account::AccountId20 mapping (Thanks to https://github.com/joelamouche)

Changes:

• Use new-gen voteLockingPeriod in democracy derives (as available)
• Dynamically inject getters for Extrinsic payloads
• Optimize caching for complex constructed type classes per registry
• Convert metadata, rpc and api to use lazy decoration
• Split u8a decoding paths for Vec (different from general path)
• Keep track of initial u8a decoded length inside base Codecs
• Extract multi property assignments for Struct, Set, Json & Enum
• Move PortableRegistry location inside @polkadot/types/metadata
• Bump static metadata for latest Substrate, Polkadot & Kusama