Make on TextLogLevel PascalCase (instead of SCREAMING CASE) to avoid clashes with preprocessor defines

[Wumpf]

What

• Fixes C++ API, DEBUG symbol conflict #4151

Considered also just using lower case on these (nobody would do #define debug, ... RIGHT?). But they are enum - like constants so all-caps felt appropriate.

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[abey79]

That was my preferred choice, so I'm gonna approve this ;)

[emilk]

Alternative: use PascalCase for constants in C++. See #4151 (comment)

[Wumpf]

Discussed this a bit more on internal Slack: there's some risk that Debug is a define as well, but we'll take that.
Our enums that are emitted for arrow union types already follow this convention so we can stick with that everywhere now

[abey79]

lgtm