Prepare api directory for udc mainline branch

udc-extended-api directory will be used only in udc mainline branch to
hide @FlaggedApi annotated api which is not supported in that branch

Copied api directories from udc mainline branch.

Bug: 299411828
Test: TH
Change-Id: I86023b1fb3e5f9b4b787a564303e6d2e60f74467
diff --git a/framework/udc-extended-api/lint-baseline.txt b/framework/udc-extended-api/lint-baseline.txt
new file mode 100644
index 0000000..2f4004a
--- /dev/null
+++ b/framework/udc-extended-api/lint-baseline.txt
@@ -0,0 +1,4 @@
+// Baseline format: 1.0
+VisiblySynchronized: android.net.NetworkInfo#toString():
+    Internal locks must not be exposed (synchronizing on this or class is still
+    externally observable): method android.net.NetworkInfo.toString()