MediaFormat: add more getters, setters as well as iterators

Add getters with default value.
Add numeric getters for arbitrary numeric format.
Add ability to enumerate and remove keys and feature keys.
Add copy constructor.
Add nullable annotations.

Bug: 112369509
Change-Id: Ifcb4ab7c4b3599aae5f6bf49001e9e8bb24b0a33
2 files changed