Gson.assertFullConsumption should throw JsonSyntaxException if JSON was not fully consumed

[Marcono1234]

Currently Gson.assertFullConsumption throws a JsonIOException if the JSON was not fully consumed:

gson/gson/src/main/java/com/google/gson/Gson.java

Lines 902 to 906 in ceae88b

	private static void assertFullConsumption(Object obj, JsonReader reader) {
	try {
	if (obj != null && reader.peek() != JsonToken.END_DOCUMENT) {
	throw new JsonIOException("JSON document was not fully consumed.");
	}

Maybe it would be better to throw a JsonSyntaxException instead, because:

• The problem is not really IO related because reading worked without issues (no IOException was thrown)
• This code is also called by fromJson(String, ...) which does not declare that it can throw a JsonIOException

For the case where a type adapter is not properly consuming all input (see also #835) neither would match perfectly though that might be acceptable.