[x11] Fix file drops from Wayland sources

[SanjoSolutions]

Summary

• keep pending Xdnd drop state alive when XWayland sends XdndLeave immediately after XdndDrop
• retry file-data selection conversion with common Wayland/XDG portal targets when text/uri-list is unavailable
• tighten URI-list parsing for CRLF, comments, localhost file URIs, and plain-path fallback payloads

Testing

• Built Aseprite with cmake --build build --target aseprite
• Installed locally and verified dragging a file from GNOME Files into an Aseprite window opens the file on Ubuntu 25.10 / GNOME 49 Wayland

Context: aseprite/aseprite#1410

[SanjoSolutions]

I have fixed the linter formatting errors.

[dacap]

Sorry @SanjoSolutions, I saw that you've used Codex to create your patch, we're not accepting PRs co-authored by AI. I'll close this PR and add a note about this in the PR template (Aseprite already have the note).

[SanjoSolutions]

Ok. I hope that it is still fixed, so other Linux users receive the same benefit. You can also copy the changes from the PR (I give you MIT-0 permissions).

While I don't care much about your choices, I would recommend to reconsider your policy and make it more reasonable.

Best regards
Jonas