Variable isShapeSpecifierKeyConst

isShapeSpecifierKey: "__vir__shape__specifier__key__do__not__use__in__actual__objects" = '__vir__shape__specifier__key__do__not__use__in__actual__objects'

A special key string which is used to tag ShapeSpecifier instances so that we know they're shape shape specifiers instead of part of the shape itself.

This should be a symbol, but TypeScript errors out about "using names that cannot be named" in that case.