Add deps attribute to flatbuffer_cc_library (#7107)

I'm not seeing the reason why we didn't attempt to support transitive
dependencies for flatbuffer_cc_library, and the current setup makes
having to propagate new dependencies to all of their recursive
dependents obnoxious.

tests/included_test.fbs

@@ -0,0 +1,3 @@
+table Wrapped {
+  a:double;
+}