Enum JSON decoding/encoding methods

[Frabat]

Hi,
when using the toJSON/fromJSON only encoding feature, I've noticed that the ts-proto outputs the serializing methods for both of them regardless which one we're using.

I wanted to track this, even though I'm already taking care and provide the PR

[Frabat]

Example:

PROTO FILE:
`message Test {
enum TestType {
TEST_TYPE_UNSPECIFIED = 0;
TEST_TYPE_EVENT = 1;
TEST_TYPE_METRIC = 2;
TEST_TYPE_DERIVED = 3;
}

}`

exported TS file:

`export interface Test {
}

export enum Test_TestType {
TEST_TYPE_UNSPECIFIED = 0,
TEST_TYPE_EVENT = 1,
TEST_TYPE_METRIC = 2,
TEST_TYPE_DERIVED = 3,
UNRECOGNIZED = -1,
}

export function test_TestTypeFromJSON(object: any): Test_TestType {
switch (object) {
case 0:
case "TEST_TYPE_UNSPECIFIED":
return Test_TestType.TEST_TYPE_UNSPECIFIED;
case 1:
case "TEST_TYPE_EVENT":
return Test_TestType.TEST_TYPE_EVENT;
case 2:
case "TEST_TYPE_METRIC":
return Test_TestType.TEST_TYPE_METRIC;
case 3:
case "TEST_TYPE_DERIVED":
return Test_TestType.TEST_TYPE_DERIVED;
case -1:
case "UNRECOGNIZED":
default:
return Test_TestType.UNRECOGNIZED;
}
}

export function test_TestTypeToJSON(object: Test_TestType): string {
switch (object) {
case Test_TestType.TEST_TYPE_UNSPECIFIED:
return "TEST_TYPE_UNSPECIFIED";
case Test_TestType.TEST_TYPE_EVENT:
return "TEST_TYPE_EVENT";
case Test_TestType.TEST_TYPE_METRIC:
return "TEST_TYPE_METRIC";
case Test_TestType.TEST_TYPE_DERIVED:
return "TEST_TYPE_DERIVED";
case Test_TestType.UNRECOGNIZED:
default:
return "UNRECOGNIZED";
}
}

export const Test = {
toJSON(_: Test): unknown {
const obj: any = {};
return obj;
},
};`

[stephenh]

Fixed in #910 , thanks @Frabat !