In this PR I have created MDCFilledTextField and MDCOutlinedTextField concrete classes that inherit from an MDCInputTextField base class. There are no significant changes to how the text fields work under the hood--they are still contained input views. However, that protocol conformance is now private. If we were to include these classes in our library clients would not need to have any idea what a Contained Input View is. For discussion on the rationale for doing this see the ill-fated https://github.com/material-components/material-components-ios/pull/6985 and [b/130306935](http://b/130306935).
Closes#7111.
* Refactor simple text field manual layout example code
* Make clear button layout calculation more understandable
* Have density informer protocol provide floating font scale factor instead of floating font size
* Send editingChanged event when clearing text
* Extract some placeholder management into a common object
* Run clang format
* Add WIP fancy animations to filled style
* In the middle of dealing with vertical density
* ITF vertical density is in a good place at the expense of ICV vertical density
* Run clang format
* Update input chip view density and example
* Add dynamic type support
* Ran clang format
* remove dead code
* Add a density informer method for the padding around the toprow/bottomrow divider
* Refactor placeholder animation code
* Ran clang format
* Refactor some placeholder layout logic
* Add nullability annotations
* Add missing nullability annotation
* Get rid of framework import for now
* Cast CAAnimation to CABasicAnimation
* Rename containerRect to containerFrame
* A bunch of property, class, and file renamings
* beginning to split floating label and placeholder. also some renamings
* Ran clang format
* More renamings
* More renamings
* Ran clang format
* A ton of renamings, some of which may need a second look ...
* More work separating floating label and placeholder
* Ran clang format
* About to make placeholder a UILabel again :(
* Placeholder and floating label are behaving pretty well together
* Fix placeholder appearance in text field
* Get rid of unneeded method
* Added some docs and got rid of the density informer method for bottom padding
* Get rid of some dead code
* Ran clang format
* Add nullability annotation
* Add CGFloat cast
* Renamed some things
* Positioning delegates no longer inherit from a root class, and they are passed into style object initializers
