fix[ux]: indexing empty literal arrays

[tserg]

What I did

Fix #4001

How I did it

• Check if reduced value is a literal list in visit_Subscript in local visitor
• Special handling for folding of dynamic arrays for empty builtin.

How to verify it

Commit message

fix: indexing empty literal array

This PR properly handles the exception for indexing into an 
empty literal array.

Description for the changelog

Cute Animal Picture

[charles-cooper]

is that an axolotl?

[tserg]

is that an axolotl?

yes ser

[charles-cooper]

maybe we should add rules for all the other types?

[tserg]

maybe we should add rules for all the other types?

do you mean to return a vyper node where possible in builtin(empty)._try_fold()?

[charles-cooper]

do you mean to return a vyper node where possible in builtin(empty)._try_fold()?

yea, we might be able to remove some ~empty things in codegen (but i'm not sure, it's been awhile since that code has been touched)