0481fa2584 util: refactor upper/lowercase functions (Karl-Johan Alm)
Pull request description:
This includes renaming Downcase() to ToLower() and make it return a string rather than modify referenced arg.
Also adds ToUpper() string version.
Additionally, it clarifies that the locale independency of the case functions is a *feature* and not a limitation. I interpreted it as the latter and rewrote code to be locale-aware before realizing this.
This is done in preparation for #11413 and as a general refactor. I don't think the optimization that the pre-refactor state gave warrants the unwieldy usage.
ACKs for top commit:
laanwj:
ACK 0481fa2584 from me
practicalswift:
ACK 0481fa2584 -- diff looks correct
l2a5b1:
ACK 0481fa2 - Although, I think @luke-jr's [feedback](https://github.com/bitcoin/bitcoin/pull/16566#issuecomment-519580760) is spot on; `Downcase` is just an artifact of `ParseNetwork`, which has been happily downcasing `net` via a string argument for over 7 years; and I do recommend to add `ToLower` *when* somebody actually needs it in new work, there is no point in keeping a trivial utility function if it is not appreciated.
promag:
ACK 0481fa2584.
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b799ebcc17