Problem:
A floating preview window (hover, signature help) converted to a normal
window (e.g. with CTRL-W_H or nvim_win_set_config()) is still closed by
the open_floating_preview() autocommands, and a later preview may focus
or close it as if it were still a float.
Solution:
When the preview window is no longer floating, remove its auto-close
autocommands and stop tracking it as the buffer's floating preview.
Closes#36659
01c4d37959