Migrate ForbiddenFunctionsCheck to CodeCheckVisitor
Migrate ForbiddenPHPFunctionsCheck to CodeCheckVisitor
Migrate VIPRestrictedClassesCheck to CodeCheckVisitor
Migrate VIPRestrictedCommandsCheck to CodeCheckVisitor, and update tests accordingly
Migrate CustomizerTest to CodeCheckTestBase
Have CustomizerTest cover use of WP_Customize_Image_Control and WP_Customize_Control classes
Migrate CustomizerCheck to CodeCheckVisitor
Migrate ForbiddenConstantsCheck to CodeCheckVisitor
Add test for ForbiddenConstantsCheck
Add test for DeprecatedConstantsCheck
Migrate DeprecatedConstantsCheck to CodeCheckVisitor
Migrate VIPParametersTest to CodeCheckTestBase, dropping pointless tests

It doesn't make any sense to create new kinds of checks on the fly
at test scope, especially not in the way this was done here. There
was e.g. a check that warned about the presence of a numeric parameter
value but only checked for the number 5 (which it was given at test
scope, thus passing the test).
Migrate VIPParametersCheck to CodeCheckVisitor
Add test for DeprecatedParametersCheck
Migrate DeprecatedParametersCheck to CodeCheckVisitor
Remove duplicates from DeprecatedFunctionsCheck
Add test for DeprecatedFunctionsCheck
Migrate DeprecatedFunctionsCheck to CodeCheckVisitor