in the language pref list (bug was no selection in the default language list).
Fix half of bug 1956707 where speech rate value as read from the settings
was translated to a ratio, which applied an improper speech rate on the
TTS engine (bug was setting a default rate makes the TTS demo unintelligible).
Moved logic to set the default value in the language pref list in a separate
private method to improve readability.
Changed default rate values so that normal is 1x and the fastest is 2x.
example after checking that the data required by the TTS engine is
properly installed.
Removed use of local constants for the the default TTS values, use
the values defined in TextToSpeech.Engine instead.
