Rename HotwordAudioStreamManager and add Javadoc

"Manager" is a little vague and "Copier" is clearer with the class's
purpose.

Bug: 258323047
Test: None with this change; simple refactoring
Change-Id: I43a24b27983838e0ef9798eef2f45d1d4b1c9ac8
Merged-In: I43a24b27983838e0ef9798eef2f45d1d4b1c9ac8
2 files changed