## Link to GitHub Issue or related Pull Request, if one exists
#287
## Description of change
Switch over to new event-based I/O system in ImGui so that we can keep
up with ImGui updates.
Unlike #287, this change does not modify how mouse position is handled.
That continues to be supported by newer versions of ImGui.
## Testing
wip
## Link to GitHub Issue, if one exists
n/a
## Description of change
Update ImGui to `v1.91.4`. We can't update to `v1.91.5` or newer just
yet because impl_spice depends on the old IO model of ImGui which got
removed in `v1.91.5`.
We also can't update the DX9 renderer right now, because at some point
overlay breaks in TDJ (and only in TDJ...)
Enable the new debug logging functionality in ImGui. Add a button in
overlay to toggle debug log window.
Fix some minor bugs spotted by the new ImGui debug log: mismatched API
calls, font loading issues.
## Compiling
👍
## Testing
In progress.
bicarus