Overwrite without confirmation when modified sketch name already exists

Using Arduino IDE 1.8.14 Hourly Build 2021/03/09 09:33, Windows 10

1. File > Save As... > save sketch as `foo_bar`
2. Modify the sketch
3. File > Save As... > save sketch as `foo+bar`

The Arduino IDE replaces the disallowed character `+` in the second filename with `_` and overwrites the existing `foo_bar` sketch without any confirmation. I would expect the IDE to require a confirmation before overwrite, as the hourly and beta builds already do when you provide an existing file name to Save As...

Reproduce the Save As sequence in Arduino IDE 1.x using the names `foo_bar` and `foo+bar`. Trace the filename sanitization and overwrite-confirmation flow; done means the second save asks for confirmation instead of silently replacing the existing sketch.

Written by the indexing model from the issue text.