Encode values when serializing android-app Intent

And decodes them when reconstructing the Intent.

Also adds methods to Uri to check whether a string is already
encoded (whether it does not contain any non-allowed characters)
which are used to enforce that values are encoded when serializing.

This does not solve the problem for generic URIs that were not
serialized using the framework APIs, as it's not possible to tell
whether or not a particular string containing invalid characters
should be encoded or not.

For example, in a query string, `key=value` might accidentally encode
the `=`, which might break some usages of Uri.Part.

This is a high risk that this will break the parsing of arbitrary
URIs which do not conform to the encoding structure the framework
APIs expect, but would otherwise work before this change.

Bug: 281848623
Bug: 281849097
Bug: 281849163

Test: atest android.content.cts.IntentEncodingParameterizedTest

Change-Id: I6e3e93247a8ac02e661d267976c7b6e7093a47c1