Fix Powerpoint say all on new slide (#17498)

Follow up of #17488

Summary of the issue:
Since #17488, entering a slide show in Power point no longer activates say all when that browse mode option is disabled. However, I intended this to also apply to cases where you'd move from one slide to another, which didn't work.

Description of user facing changes
NO say all when moving from slide to slide in a slide show and the browse mode option is disabled.

Description of development approach
Expanded the reportSlide method.

source/appModules/powerpnt.py

@@ -1387,18 +1387,9 @@ def __contains__(self, obj):
 	def event_treeInterceptor_gainFocus(self):
 		braille.handler.handleGainFocus(self)
 		self.rootNVDAObject.reportFocus()
-		doSayAll = not self.hadFocusOnce and config.conf["virtualBuffers"]["autoSayAllOnPageLoad"]
+		self.reportNewSlide(self.hadFocusOnce)
 		if not self.hadFocusOnce:
 			self.hadFocusOnce = True
-		if doSayAll:
-			self.reportNewSlide()
-		else:
-			info = self.selection
-			if not info.isCollapsed:
-				speech.speakPreselectedText(info.text)
-			else:
-				info.expand(textInfos.UNIT_LINE)
-				speech.speakTextInfo(info, reason=controlTypes.OutputReason.CARET, unit=textInfos.UNIT_LINE)
 
 	def event_gainFocus(self, obj, nextHandler):
 		pass
@@ -1408,9 +1399,22 @@ def event_gainFocus(self, obj, nextHandler):
 	def makeTextInfo(self, position):
 		return self.TextInfo(self, position)
 
-	def reportNewSlide(self):
-		self.makeTextInfo(textInfos.POSITION_FIRST).updateCaret()
-		sayAll.SayAllHandler.readText(sayAll.CURSOR.CARET)
+	def reportNewSlide(self, suppressSayAll: bool = False):
+		"""Reports a new slide, activating say all when appropriate.
+		:param suppressSayAll: When say all should be suppressed always, e.g.
+			because tree interceptor gets focus multiple times.
+		"""
+		doSayAll = not suppressSayAll and config.conf["virtualBuffers"]["autoSayAllOnPageLoad"]
+		if doSayAll:
+			self.makeTextInfo(textInfos.POSITION_FIRST).updateCaret()
+			sayAll.SayAllHandler.readText(sayAll.CURSOR.CARET)
+		else:
+			info = self.selection
+			if not info.isCollapsed:
+				speech.speakPreselectedText(info.text)
+			else:
+				info.expand(textInfos.UNIT_LINE)
+				speech.speakTextInfo(info, reason=controlTypes.OutputReason.CARET, unit=textInfos.UNIT_LINE)
 
 	@scriptHandler.script(
 		description=_(