Introduce EditorInfo#locales.

The primary goal of this CL is to enable application developers to
provide more context-based language (locale) information for IME
developers so that users can be benefited by more natural text input
experience.

As of API Level 23, there are several APIs that allow IMEs to retrieve
locale/country related information.

  - Locale#getDefault()
  - Configuration#locale
  - LocaleSpan#getLocale()
  - SubscriptionInfo#getCountryIso()

However, only LocaleSpan#getLocale() can be used to pass application
specific languge (locale) context from applications to IMEs.  Also
LocaleSpan is not designed to be used per input-context.  We want to
have something in EditorInfo and LocaleList would be the right thing.

Although default implementation of TextView#onCreateInputConnection()
starts filling EditorInfo#localeList with TextView#getTextLocales() by
this CL, application developers are encouraged to provide its own
LocaleList when they are confident that the user want to use a
certain (set) of language(s).

For instance, a chat application may be able to guess what language will
be used in the conversation before the user start typing.  At least it
should be able to remember the last used language for each conversation.

Another instance would be "From" and "To" EditText fields in a
translation app.  Those fields should have different LocaleList based on
the languages that the user want to translate from and to.

Bug: 22859862
Change-Id: I77db5b99a7cf745d800db75baf135bb60ad04820