Need a function to perform UTS35 3.3.1 BCP 47 Language Tag to Unicode BCP 47 Locale Identifier

Currently there are no code to perform the UTS35 3.3.1 BCP 47 Language Tag to Unicode BCP 47 Locale Identifier canonicalization as stated in
http://unicode.org/reports/tr35/#Language_Tag_to_Locale_Identifier

Since the implementation need to read in resource from "metadata", we should add a new class to implement such canonicalization.

See
icu4j/tools/misc/src/com/ibm/icu/dev/tool/locale/LikelySubtagsBuilder.java
icu4j/main/classes/core/src/com/ibm/icu/util/Region.java
icu4c/source/i18n/region.cpp
for examples of how to read the "replacement" from metadata/alias/{language,territory}