[CLEANUP] Tidy up DeclarationBlock::parse()

[JakeQZ]

• Assign the result of ParserState::peek() to a local variable, for efficiency;
• Use a switch statement to branch on its value, for extensibility (e.g. [BUGFIX] Allow comma-separated arguments in selectors #1292);
• Don't unnecessarily test that a quote character is not escaped when not within a string.

[coveralls]

coverage: 57.935% (+0.03%) from 57.906%
when pulling 5826c8b on cleanup/declarationblock-parse
into 11e634c on main.

[oliverklee]

While we're at it, let's move the changed parts to nullable strings instead of set/not-set variables.

[JakeQZ]

While we're at it, let's move the changed parts to nullable strings instead of set/not-set variables.

I've accepted all suggestions :)

[oliverklee]

The red builds look like some PHIVE install hiccup. I've kicked the pipeline.

[oliverklee]

This might also fix a PHPStan warning - so we might need to regenerate the baseline.

[JakeQZ]

This might also fix a PHPStan warning - so we might need to regenerate the baseline.

It does, but also $stringWrapperCharacter needs to be initialized in order to use is_string instead of isset. Should be OK now.