Pass rpc/mining RPC argument descriptions to RPCHelpMan

Summary:
PR14796 changes the help text of the dummy argument in
prioritisetransaction from optional to required. PR14785 was added to
prevent this.

Merge #14875: RPCHelpMan: Support required arguments after optional ones

fa9a5bc1a0 RPCHelpMan: Support required arguments after optional ones (MarcoFalke)

Pull request description:

There was a requirement that required arguments could not be positioned after an optional argument, but the deprecation of priority made the second argument to `prioritisetransaction` optional. So support that in `RPCHelpMan`.

Also format all named arguments in the same way (without the wrapping `"` even for strings), since the extended description already mentions the type and it feels odd to special case strings.

Tree-SHA512: c125145afb4a63abc995aaf0a89489efc0f470a720727a1ca6ee0bfd2bcbc59e87c38128dd1e0cdf03dbb5b18e84867887c3dabf6ec8378e66cb1f4cecb9e407

Partial backport of Core PR14796 and PR14875

Test Plan:

mkdir master
mkdir patched

On master:

ninja
./bitcoind
./bitcoin-cli help > RPCs
./getrpchelps.sh RPCs master

On the patched branch:

ninja
./bitcoind
./getrpchelps.sh RPCs patched
./checkrpc.sh RPCs master patched D5714diff

Verify the changes in D5714diff.

Scripts:

D5714diff:

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5714