aconfig: allow dots in package fields

Allow package fields to include dots.

Update the generated code based on the package name: if the package name
is com.android.example:

  - java: package com.android.example; ...
  - C++: namespace com::android::example { ... }
  - Rust: mod com { mod android { mod example { ... } } }

Also, update examples to use dots in the package fields.

Also, remove unnecessary #include from the auto-generated C++ code: the
header should not include itself.

Bug: 285000854
Test: atest aconfig.test
Change-Id: I8a5352e25c64c34dee0725202a1b7c9957819de8
diff --git a/tools/aconfig/templates/java.template b/tools/aconfig/templates/java.template
index 44c470c..709af44 100644
--- a/tools/aconfig/templates/java.template
+++ b/tools/aconfig/templates/java.template
@@ -1,4 +1,4 @@
-package aconfig.{package};
+package {package};
 {{ if readwrite }}
 import android.provider.DeviceConfig;
 {{ endif }}