* Add the Truth dependency
* Port Junit test to Truth in the package `com.google.gson` of the module `gson`
* Replace the `assertThat(e.getMessage()).isEqualTo(...)"` with `assertThat(e).hasMessageThat().isEqualTo(...)`
* Minor fixes
* Make Object and JsonElement deserialization iterative
Often when Object and JsonElement are deserialized the format of the JSON
data is unknown and it might come from an untrusted source. To avoid a
StackOverflowError from maliciously crafted JSON, deserialize Object and
JsonElement iteratively instead of recursively.
Concept based on 51fd2faab7
But implementation is not based on it.
* Improve imports grouping
* Address review feedback
Éamonn McManus