Split `trait Extrinsic` into logical components (#3736)

Fixes #3571 

Built on top of #3685.

This PR breaks up `trait Extrinsic` into different self-contained
interfaces as follows:
- `ExtrinsicLike` for querying the type of extrinsic (signed/unsigned)
- `CreateTransaction` for creating a transaction (general)
- `CreateSignedTransaction` for creating a signed transaction
(old-school)
- `CreateInherent` for creating an inherent

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Signed-off-by: georgepisaltu <[email protected]>
Co-authored-by: command-bot <>