Method fromJson throws JsonParseException instead of declared JsonSyntaxException

# Gson version

I found a bug in GSON library. It's actual fo version 2.12.1

# Description

Bug description:

Method fromJson signature looks like that:
```
public T fromJson(String json, Class classOfT) throws JsonSyntaxException {
```

so, it's obvious to coders to catch JsonSyntaxException:
```
try {
goodGson.fromJson(badJson, User.class);
} catch (JsonSyntaxException e) {
System.out.println("Good deserializer caught JsonSyntaxException");
}
```
Such construction works until we add Deserializer:
```
Gson badGson = new GsonBuilder()
.registerTypeAdapter(User.class, new UserBadDeserializer())
.create();

class UserBadDeserializer implements JsonDeserializer {
@Override
public User deserialize(JsonElement json, Type typeOfT,
JsonDeserializationContext context) throws JsonParseException {
JsonObject jsonObject = json.getAsJsonObject();
if (!jsonObject.has("name"))
throw new JsonParseException("json should contain the name field!");
String name = jsonObject.get("name").getAsString();
return new User(name);
}
}
```
The signature of deserialize method we should override, throws another
exception - JsonParseException, which is parent to JsonSyntaxException
and isn't caught by try-catch construction above
It flies further and may cause unexpected behaviour.

```
try {
try {
badGson.fromJson(badJson, User.class);
} catch (JsonSyntaxException e) {
System.out.println("Good deserializer caught JsonSyntaxException");
}
} catch (RuntimeException e) {
System.out.println("Bad deserializer didn't catch JsonSyntaxException, and "
+ e.getClass().getSimpleName() + " flew further");
}
```
Solution 1 : Change signature of deserialize method to throw JsonSyntaxException.

Solution 2 : Change signature of fromJson method (and other methods calling
deserialize) to throw JsonParseException.

I've made a simple example to show this bug:
https://github.com/DGorokhov123/gson-bug

(С) Dmitriy Gorokhov dgorokhov123@gmail.com, @DGorokhov123