wallet: descriptor wallet cleanups

Summary:

rpc: createwallet warning that descriptor wallets are experimental

Remove unimplemented SetCrypted from DescriptorScriptPubKeyMan

Change SetType to SetInternal and remove m_address_type

m_address_type was used for two things:

1. Determine the type of descriptor to generate during SetupDescriptorGeneration
2. Sanity check during GetNewDestination.

There is no need to have this variable to accomplish those things.

1. Add a argument to SetupDescriptorGeneration indicating the address type to use
2. Use Descriptor::GetOutputType for the sanity check.

This is a backport of Core PR18787

It does not include the release notes from the original backport.

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9236