[TRACKER] Regressions with sokol backend

[serkonda7]

Collection of remaining problems with the new sokol backend.

• [ ] Textbox problems (https://github.com/vlang/ui/issues/203)

• [ ] Password text input display extra trailing chars and have cursor flickering (users.v)

• [ ] message box ok button does not work (message.v)

• [ ] Closing a message box closes all windows (users.v)

• [ ] Checkboxes do not work (users.v)

• [ ] Sliders cannot be dragged by mouse (https://github.com/vlang/ui/issues/207)

• [ ] Resizing is always enabled and resizable has no effect (https://github.com/vlang/ui/issues/231) (https://github.com/floooh/sokol/issues/380)

[serkonda7]

Done

• [x] set_title is not implemented (missing in sokol) (change_title.v)
• [x] Images are flipped over (users.v counter.v)
• [x] Images are not rendered (users.v counter.v)
• [x] Textboxes do not accept input
• [x] Wrong alignment of text in buttons
• [x] Missing text width calculation