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.
