patch 8.2.3996: Vim9: type checking lacks information about declared type

patch 8.2.3996: Vim9: type checking lacks information about declared type

Problem:    Vim9: type checking for list and dict lacks information about
            declared type.
Solution:   Add dv_decl_type and lv_decl_type.  Refactor the type stack to
            store two types in each entry.