Add automatic background braille display detection (#7741)

* Implement braille display auto detection. This new background mechanism can be activated by choosing the Automatic option from NVDA's braille display settings. See #1271 for an in depth discussion of funcionality.

* brailliantB, use generic implementation for USB serial devices
* Use generic check function for braille display drivers supporting bdDetect
* Make auto detection the default
* Set a timeout for joining the bgThread when auto detection was on
* Poll for bluetooth devices on app switches
* Support bluetooth HID in bdDetect

* Use a separate thread for background scanning.

* Make the bdDetect thread a daemon thread

* Disable auto detection within the unit test framework. If we don't do this, detection will occur and unit tests will fail.

* in braille.handler.handleGainFocus, check whether the focused object has an active tree interceptor. If so, focus the tree interceptor instead

* Revert the use a separate thread for background scanning and make sure recursion does not occur when using an APC

This reverts commit 5b97f39.

* Created Detector._scanQueuedSafe which wraps changing the state of _scanQueued within a lock

* Fix malformed VID and PID for Brailliant, add an extra check

* NO longer filter serial ports for Brailliant

* Updated changes.t2t

source/appModuleHandler.py

@@ -33,13 +33,20 @@
 import api
 import appModules
 import watchdog
+import extensionPoints
 
 #Dictionary of processID:appModule paires used to hold the currently running modules
 runningTable={}
 #: The process ID of NVDA itself.
 NVDAProcessID=None
 _importers=None
 _getAppModuleLock=threading.RLock()
+#: Notifies when another application is taking foreground.
+#: This allows components to react upon application switches.
+#: For example, braille triggers bluetooth polling for braille displaysf necessary.
+#: Handlers are called with no arguments.
+post_appSwitch = extensionPoints.Action()
+
 
 class processEntry32W(ctypes.Structure):
 	_fields_ = [
@@ -237,6 +244,9 @@ def handleAppSwitch(oldMods, newMods):
 	processed = set()
 	nextStage = []
 
+	if not oldMods or oldMods[-1].appName != newMods[-1].appName:
+		post_appSwitch.notify()
+
 	# Determine all apps that are losing focus and fire appropriate events.
 	for mod in reversed(oldMods):
 		if mod in processed: