Physical movement and other events on some newer computers are no longer treated as inappropriate key presses. Previously, this silenced speech and sometimes triggered NVDA commands.

Some devices notify about these events using non-standard scan codes, for which GetKeyNameText returns inappropriate names. These report a vk code of 0xFF, so handle this appropriately.
These will now report as unknown in input help mode and can be mapped as gestures if desired using the log.
Re #3468.
When reporting unknown scan codes in input help, include the scan code.

This won't be meaningful to the user, but at least they'll understand when different keys (real or fake) are being sent.
Also, make sure the code part is always two digits, even if it only needs to be one, as that makes it clearer that it's a code.
Re #3468.
Merge branch 't3468'. Fixes #3468
Merge commit 'fetch_head' into jpbranch