Reland union type

[webfiltered]

• Relands Add union link connection type support #5806
• Resolves Support wildcard type "*" in ComfyUI core #5890
• Resolves comment in issue Support wildcard type "*" in ComfyUI core #5890 (comment)
• Now uses almost(*) identical logic to former behaviour if types match:
  • If types matched before this PR, they will still match
  • If they do not match:
    • Check both types are string
    • Perform new union type check

(*) Only changes are one function call and a not not conversion

[huchenlei]

LGTM. Thanks for tracing this down!