Fix Room Index name docs markdown swallowing underscores - #891

https://developer.android.com/reference/androidx/room#getName()

In the resulting documentation page, the underscores used in the description were interpreted as markdown and thus not displayed as characters documenting the generated index name. Use of backticks preserves them and will display as intended when run through the markdown converter.

Additionally, a correction (assuming the worked example is correct) is included when describing the prefix.

Proposed Changes

• Use backticks in the method description to preserve underscore literals in output HTML
• Add missing underscore in the described prefix after table name

Testing

Test: None; this is a documentation change.