feat(theme_tailor, theme_tailor_annotation): Add @TailorMixin

[Rongix]

Changes:

• Add alternative generator: @TailorMixin allows for different code style to define ThemeExtension classes, it requires a bit more boilerplate code than @Tailor and doesn't allow to instantly define themes but there are some benefits:
  • More control over defined ThemeExtension class, adding methods, static properties etc
  • Easier refactoring, any code you write that depends on these classes will get refactored properly
  • More familiar syntax to vanilla classes
  • All of the code is used and not discarded, for some cases in @Tailor annotated class would be left unused and it requires adding ignore lint flags (for unused elements etc)

Source changes:

• Add utilities to treat 2 generators separately,
• Add new templates for @TailorMixin generation, some of the code can be reused in the future (especially for hash code and equality) but there are quite important differences how 2 generators operate and generate code therefore I didn't cover it in this PR