Refine A11y Tile Service javadoc

- Explicitly say that this is only the class name,to be looked up in the a11y services package, and not a full component name
- Fix typo of Javadoc refers to class names (plurar)
- Rename to getTileServiceName()

Bug: 219873375
Test: atest AccessibilityShortcutInfoTest
Change-Id: Ic7231f6e0b34edabea8b4086102e1d7f6ebe0eae