ChatScreenMixin Refactor/Compat

[matthewperiut]

This commit maintains functionality, while improving readability and compatibility with mixins into the same class.
Before this commit compatibility with SPC 0.4.0 was poor due to this mixin.

[js6pak]

This change would mean that mojangfix has to maintain text input patches in 2 places (TextFieldWidgetMixin and ChatScreenMixin). The problem with that approach is that you can forget to implement all features in all places, which is exactly what happened in this PR: HOME/END keys no longer work.
Looking at spc-babric patches they look too complex to handle compatibility cleanly without either making it hard depend on mojangfix or making it disable mojangfix ChatScreen mixins.

[matthewperiut]

You're right about that, I made large changes without considering all the effects.