Review all sniffs/code doing label name comparisons

Bug Description

Label names, i.e. names of namespaces, class/trait/interface/enum name and function names are case-insensitive for the ASCII letters, but case-sensitive for char 0x80 and up.

For the record: variable names in PHP are case-sensitive and so are constant names (unless explicitly declared not to be so via define()).

There are a number of sniffs in PHP_CodeSniffer which compare names, be it comparing a class name with another class name (Generic.Classes.DuplicateClassName), be it comparing a class name with a method name (Generic.NamingConventions.ConstructorName).

I'm fairly sure that, in most cases, these comparisons will use code akin to strtolower($nameA) === strtolower($nameB). This is incorrect and these comparisons should be fixed to use strcasecmp() instead, as strcasecmp() only compares the ASCII letters case-insensitively (which is exactly what is needed).

Notes about this task:

Code in sniffs checking the case of keywords using strtolower() does not need to be changed as PHP does not contain any keywords containing non-ASCII characters.
Code in sniffs checking the case of PHP native label names using strtolower() does not need to be changed as PHP does not contain any functions/classes etc containing non-ASCII characters.
Any JS/CSS-only sniffs can be ignored for the purposes of this task as they will be removed in PHPCS 4.0 anyway.
Sniffs from the MySource standards can be ignored for the purposes of this task as they will be removed in PHPCS 4.0 anyway.

Task List

The below is a list of sniffs in which strtolower() was found and which need to be reviewed.

Each of these will need to be reviewed, though I expect that by far not all of them will need changes.

To do

[ ] Generic.Classes.DuplicateClassName
[ ] Generic.Classes.OpeningBraceSameLine
[ ] Generic.CodeAnalysis.EmptyStatement
[ ] Generic.CodeAnalysis.UnusedFunctionParameter
[ ] Generic.Files.LowercasedFilename
[ ] Generic.NamingConventions.AbstractClassNamePrefix
[ ] Generic.NamingConventions.CamelCapsFunctionName
[ ] Generic.NamingConventions.ConstructorName
[ ] Generic.NamingConventions.InterfaceNameSuffix
[ ] Generic.NamingConventions.TraitNameSuffix
[ ] Generic.NamingConventions.UpperCaseConstantName
[ ] Generic.PHP.ForbiddenFunctions
[ ] Generic.PHP.LowerCaseConstant
[ ] Generic.PHP.LowerCaseKeyword
[ ] Generic.PHP.LowerCaseType
[ ] Generic.PHP.RequireStrictTypes
[ ] Generic.PHP.SAPIUsage
[ ] Generic.PHP.UpperCaseConstant
[ ] Generic.WhiteSpace.LanguageConstructSpacing
[ ] Generic.WhiteSpace.ScopeIndent
[ ] PEAR.Classes.ClassDeclaration
[ ] PEAR.Commenting.ClassComment
[ ] PEAR.Commenting.FileComment
[ ] PEAR.Commenting.FunctionComment
[ ] PEAR.Functions.FunctionDeclaration
[ ] PEAR.Functions.ValidDefaultValue
[ ] PEAR.NamingConventions.ValidFunctionName
[ ] PSR1.Classes.ClassDeclaration
[ ] PSR1.Files.SideEffects
[ ] PSR1.Methods.CamelCapsMethodName
[ ] PSR12.Files.DeclareStatement
[ ] PSR12.Files.FileHeader
[ ] PSR12.Files.ImportStatement
[ ] PSR12.Keywords.ShortFormTypeKeywords
[ ] PSR12.Traits.UseDeclaration
[ ] PSR2.Classes.ClassDeclaration
[ ] PSR2.ControlStructures.SwitchDeclaration
[ ] Squiz.Arrays.ArrayDeclaration
[ ] Squiz.Classes.ClassDeclaration
[ ] Squiz.Classes.LowercaseClassKeywords
[ ] Squiz.Commenting.FunctionComment
[ ] Squiz.ControlStructures.ForEachLoopDeclaration
[ ] Squiz.ControlStructures.LowercaseDeclaration
[ ] Squiz.ControlStructures.SwitchDeclaration
[ ] Squiz.Functions.LowercaseFunctionKeywords
[ ] Squiz.Operators.ValidLogicalOperators
[ ] Squiz.PHP.LowercasePHPFunctions

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If the file does not need changes, report back saying so, so it can be moved to "Done".
If the file does need changes, please accompany the changes by tests. The tests should safeguard that names containing only ASCII characters, but in a different case, compare as "equal" and names containing non-ASCII characters in a different case do not compare as "equal".

PRs related to this task should preferably only address one file - or even one instance of the issue in one file - per PR. This will make reviewing the changes more straight forward and will allow for merging PRs promptly.

PHPCSStandards / PHP_CodeSniffer