Implement json decoding for Any message. (#130)

* Implement json decoding for Any message.

type url may not appear as the first value in json. As a result,
other data cannot be resolved before resolving type url. To solve that,
this change caches the start and end position of unparsed values and
resolve them in end_any_object when type url has been resolved.

* Handle Any in switch

* Update json parser size

* Fix comments

* Sync upstream

* Add dependency on upb_pb for upb_json

* Debug failed test

* Fix cmake

* Update test generated files

* Remove debug tests

BUILD

diff --git a/BUILD b/BUILD
index 97380a4..6233b6b 100644
--- a/BUILD
+++ b/BUILD
@@ -115,7 +115,10 @@
         "-pedantic",
         "-Wno-long-long",
     ],
-    deps = [":upb"],
+    deps = [
+        ":upb",
+        ":upb_pb",
+    ],
 )
 
 cc_library(