Make time picker accessible (#13152)

* make time picker accessible

* use new CustomPaint a11y API

* flutter_localizations tests; use bigger distance delta

* fix am/pm control; selected values

* fix translations; remove @mustCallSuper in describeSemanticsConfiguration

* exclude AM/PM announcement from iOS as on iOS the label is read back automatically
diff --git a/packages/flutter_localizations/lib/src/l10n/material_it.arb b/packages/flutter_localizations/lib/src/l10n/material_it.arb
index a0faf2a..785e32a 100644
--- a/packages/flutter_localizations/lib/src/l10n/material_it.arb
+++ b/packages/flutter_localizations/lib/src/l10n/material_it.arb
@@ -27,5 +27,7 @@
   "selectAllButtonLabel": "SELEZIONA TUTTO",
   "viewLicensesButtonLabel": "VISUALIZZA LICENZE",
   "anteMeridiemAbbreviation": "AM",
-  "postMeridiemAbbreviation": "PM"
+  "postMeridiemAbbreviation": "PM",
+  "timePickerHourModeAnnouncement": "Seleziona ore",
+  "timePickerMinuteModeAnnouncement": "Seleziona minuti"
 }