Expose uloc_getDefault()

And add a CTS Test

Bug: 160350521
Test: atest CtsIcu4cTestCases
Change-Id: I2a0118108fabcd0e5772b314e60586f9e4b5017b
diff --git a/libicu/libicu.map.txt b/libicu/libicu.map.txt
index 8e46abb..12f30b6 100644
--- a/libicu/libicu.map.txt
+++ b/libicu/libicu.map.txt
@@ -133,6 +133,7 @@
     uloc_getBaseName;
     uloc_getCharacterOrientation;
     uloc_getCountry;
+    uloc_getDefault;
     uloc_getDisplayCountry;
     uloc_getDisplayKeyword;
     uloc_getDisplayKeywordValue;