(SOLVER V2) Table indexing does not properly handle metatables.

[hardlyardi]

When indexing a table's field which can be nil, the type solver does not consider an __index value:

local nya: setmetatable<{
	meow: string?,
}, {
	__index: {
		meow: string,
	},
}>
-- TypeError: Type 'string?' could not be converted into 'string'
local purr: string = nya.meow