Merge bitcoin/bitcoin#26612: refactor: RPC: pass named argument value as string_view

545ff924ab6303ffabd91fdfc4f0a4962daf133c refactor: use string_view for RPC named argument values (stickies-v)
7727603e44f8f674e0fc8389e78047e2b56e6052 refactor: reduce unnecessary complexity in ParseNonRFCJSONValue (stickies-v)
1d02e599012721549d4c20b1b37fcc5ee7b961b6 test: add cases to JSON parsing (stickies-v)

Pull request description:

  Inspired by MarcoFalke's [comment](https://github.com/bitcoin/bitcoin/pull/26506#discussion_r1036149426). Main purpose of this PR is to minimize copying (potentially large) RPC named arguments when calling `.substr()` by using `std::string_view` instead of `std::string`. Furthermore, cleans up the code by removing unnecessary complexity in `ParseNonRFCJSONValue()` (done first to avoid refactoring required to concatenate `string` and `string_view`), updates some naming and adds a few test cases. Should not introduce any behaviour change.

  ## Questions
  - ~Was there actually any merit to `ParseNonRFCJSONValue()` surrounding the value with brackets and then parsing it as an array? I don't see it, and the new approach doesn't fail any tests. Still a bit suspicious about it though.~
    - Cleared up by https://github.com/bitcoin/bitcoin/pull/26506#pullrequestreview-1211984059
    - If there are no objections to 7727603e44f8f674e0fc8389e78047e2b56e6052, I think we should follow up with a PR to rename `ParseNonRFCJSONValue()` to a local `Parse()` helper function (that throws if invalid), remove it from `client.h` and merge the test coverage we currently have on `ParseNonRFCJSONValue()` with the coverage we have on `UniValue::read()`.

ACKs for top commit:
  ryanofsky:
    Code review ACK 545ff924ab6303ffabd91fdfc4f0a4962daf133c
  MarcoFalke:
    review ACK 545ff924ab6303ffabd91fdfc4f0a4962daf133c 📻

Tree-SHA512: b1c89fb010ac9c3054b023cac1acbba2a539a09cf39a7baffbd7f7571ee268d5a6d98701c7ac10d68a814526e8fd0fe96ac1d1fb072f272033e415b753f64a5c

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