fix(typescript-estree): add ExportDefaultDeclaration to union DeclarationStatement

[ndelangen]

I have this example:

https://astexplorer.net/#/gist/2c50aae34bea149fc9863a2dd0e7a6f5/69d563ee31f1bc01d3cf71c005bb92dd24c3910e

Notice how

export default class Foo {}

Is transformed to:

{
      "type": "ExportDefaultDeclaration",
      "declaration": {
        "type": "ClassDeclaration",
        "id": {
          "type": "Identifier",
          "name": "Foo",
          "range": [
            580,
            583
          ],
          "loc": {
            "start": {
              "line": 30,
              "column": 21
            },
            "end": {
              "line": 30,
              "column": 24
            }
          }
        },
        "body": {
          "type": "ClassBody",
          "body": [],
          "range": [
            584,
            586
          ],
          "loc": {
            "start": {
              "line": 30,
              "column": 25
            },
            "end": {
              "line": 30,
              "column": 27
            }
          }
        },
        "superClass": null,
        "range": [
          574,
          586
        ],
        "loc": {
          "start": {
            "line": 30,
            "column": 15
          },
          "end": {
            "line": 30,
            "column": 27
          }
        }
      },
      "range": [
        559,
        586
      ],
      "loc": {
        "start": {
          "line": 30,
          "column": 0
        },
        "end": {
          "line": 30,
          "column": 27
        }
      }
    }

according to Program.body which is a Statement[]

and Statement containing DeclarationStatement

I conclude that DeclarationStatement is missing ExportDefaultDeclaration

[ndelangen]

I'm contributing 'in the 'dark', if this is wrong, no hard feelings, if this commit needs to be changed to conform to something 👍

[ndelangen]

I found this by trying this:

if (i.type === AST_NODE_TYPES.ExportDefaultDeclaration) {
}

where i is a Program["body"]

which resulted in a typescript error:

This condition will always return 'false' since the types 'AST_NODE_TYPES.BlockStatement | AST_NODE_TYPES.BreakStatement | AST_NODE_TYPES.ClassDeclaration | AST_NODE_TYPES.ClassExpression | AST_NODE_TYPES.ContinueStatement | AST_NODE_TYPES.DebuggerStatement | AST_NODE_TYPES.DoWhileStatement | AST_NODE_TYPES.EmptyStatement | AST_NODE_TYPES.ExportAllDeclaration | AST_NODE_TYP...' and 'AST_NODE_TYPES.ExportDefaultDeclaration' have no overlap.ts(2367)