Fixed php-cs-fixer crashes on input file syntax error

[GrahamCampbell]

1. Some tokenizing lintier errors on PHP 7.0-7.2 cause the entire PHP process to fatal error. This was fixed in PHP 7.3, and so we should only use this linter on PHP 7.3 (catching the new type of error it can raise, instead of crashing).
2. The above change highlighted the fact that some of the code samples in the tests are only valid on PHP 5, or are not valid at all. Those that are not valid on PHP 7, but are valid on PHP 5, I've updated to only run on PHP 5. Those that are not valid syntax, but can be corrected, I have corrected. Those that are just totally incorrect, have been removed.

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Closes #5067.

[GrahamCampbell]

Friendly ping @SpacePossum.

[SpacePossum]

Thank you @GrahamCampbell ! Great to see this fixed, lots of nice fixes, much appreciated 👍

Sorry for the wait, finally got a way to test on multiple PHP versions locally. FYI I've rebased and squashed your branch.

[GrahamCampbell]

Did you remove the extra spaces in the error message? I added them to match the format from the native linter, which has two spaces after the colon.

[SpacePossum]

I did indeed, however all tests did pass on the CI and local, you think this is going to be an issue somewhere?

[GrahamCampbell]

I just left it in for consistency. Maybe we could remove the double spaces from the native linter?

[SpacePossum]

Sounds good, we don't have a BC promise on exception messages anyway. Can you PR it or maybe link the related code than I can do it later on?

[GrahamCampbell]

Oh, you changed the message prefix too? I specifically had it so it matched the native linter output.

[GrahamCampbell]

#5174 should address the issues, ensuring consistent error messages.