Allow exporting enums from GDScript

[bojidar-bg]

Examples:

enum Tile {TILE_AIR = 0, TILE_BLOCK, TILE_ICE}
export(Tile) var tile_type = TILE_AIR

export({user = 0, moderator = 50, admin = 100}) var role = 100
export({"user": 0, "moderator": 50, "admin": 100}) var role_alt = 100

const Utils = {"Util 1": 0, "Util 2": 1, "Util 3": 10}
export(Utils) var util

Closes #12392

[akien-mga]

MSVC doesn't like those:

scene\gui\tree.cpp(158): error C2065: 'INT32_MAX': undeclared identifier
scene\gui\tree.cpp(159): error C2065: 'INT32_MIN': undeclared identifier

[bojidar-bg]

Eh? Just don't use MSVC 😉

[akien-mga]

Needs rebase after #12969, sorry :)