Mapped-type creating redundant intermediary definition (--aliasRefs)

[HoldYourWaffle]

Possibly related to #232, although this seems more complicated than that.

Given the following TypeScript:

enum MyEnum { MY, AWESOME, ENUM }
type MappedType = { [key in MyEnum]?: string };

interface Type {
	map: MappedType;
}

The following schema is generated (with --aliasRefs):

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "definitions": {
        "MappedType": {
            "$ref": "#/definitions/__type"
        },
        "__type": {
            "properties": {
                "0": {
                    "type": "string"
                },
                "1": {
                    "type": "string"
                },
                "2": {
                    "type": "string"
                }
            },
            "type": "object"
        }
    },
    "properties": {
        "map": {
            "$ref": "#/definitions/MappedType"
        }
    },
    "type": "object"
}

As you can see there's a "intermediary" (and very much redundant) definitions created for the mapped type (__type). The actual MappedType definition references this definition.
No seperate enum definition is created, which makes sense because it's never truly referenced. If I do create an explicit reference the enum is generated correctly.

[HoldYourWaffle]

It should also be noted that type aliases used in the mapped type aren't preserved either, the following TypeScript results in the same schema as in the initial comment:

/** @minLength 1 */
type Word = string;

enum MyEnum { MY, AWESOME, ENUM }
type MappedType = { [key in MyEnum]?: Word };

interface Type {
	map: MappedType;
}

Should I create a separate issue for this?

[HoldYourWaffle]

This might be related to vega/ts-json-schema-generator#30.