Moved Cronet code under Connectivity

$ cp -r Cronet/ Connectivity/
$ rm -r Cronet/*

Bug: 251054736
Test: atest CronetApiTest
Change-Id: I25d5238fe530ffaa830ce64c67b351d40b8030ea
CTS-Coverage-Bug: 251012627
diff --git a/Cronet/api/system-current.txt b/Cronet/api/system-current.txt
new file mode 100644
index 0000000..d802177
--- /dev/null
+++ b/Cronet/api/system-current.txt
@@ -0,0 +1 @@
+// Signature format: 2.0