AdbKeyboard would copy the event into its own fields and set the
changed field, so that we could return the event when register was 0.
However, if a subsequent event was received before ADB polling, the
previous event would be overwritten and lost.
Fix this by maintaining a queue of events, so that we can return
everything since the last poll.
We were using an empty value on the second byte of the ADB keyboard
register 0, but that maps to the "a" key. This manifested itself
as the Key Caps DA never showing the "a" key as being down.
Switch to a non-existent key for the second byte.
Besides generating KeyboardEvents in the SDL event handler and
returning the key state in the register 0 reads of the AdbKeyboard
device, we also needed to generalize the ADB bus polling a bit. We now
check all devices that have the service request bit set, instead of
hardcoding the mouse.
The SDL key event -> ADB raw key code mapping is based on BasiliskII/
SheepShaver's, but cleaned up a bit.
Result of running IWYU (https://include-what-you-use.org/) and
applying most of the suggestions about unncessary includes and
forward declarations.
Was motivated by observing that <thread> was being included in
ppcopcodes.cpp even though it was unused (found while researching
the use of threads), but seems generally good to help with build
times and correctness.
