Add constant visibility for PSR-12 compatiblity

[hailwood]

Description

Makes the enum:make command add the public visibility keyword to all generated constants.

Motivation and context

https://www.php-fig.org/psr/psr-12/#43-properties-and-constants

How has this been tested?

Updated test cases

Types of changes

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[hailwood]

I did this quickly online, so of course the commits are a bit dirty. Good thing Github has the Squash merge option ;)

[slavarazum]

If we will provide PSR-12 compatibility, it should require all PSR-12 rules. For now, we haven't automated tools to check it.

[hailwood]

That's probably a fair point. I wasn't actually meaning PSR-12 compat for the library, just for the generated enums. This was the only thing PhpStorm flagged on the generated files after enabling the PSR-12 ruleset.

I guess we could try running styleci or PHPCS over the fixtures for the tests to verify PSR-12 compatibility.