Add dynamic display id associations for keyboards

Bug: 184615313
Test: atest -a inputflinger_tests and atest -a libinput_tests
Change-Id: I96eb6af186e001ff37d90db2436c7d60a269d4bf
diff --git a/services/inputflinger/reader/include/InputDevice.h b/services/inputflinger/reader/include/InputDevice.h
index b2b23e5..291f105 100644
--- a/services/inputflinger/reader/include/InputDevice.h
+++ b/services/inputflinger/reader/include/InputDevice.h
@@ -169,6 +169,7 @@
     uint32_t mSources;
     bool mIsExternal;
     std::optional<uint8_t> mAssociatedDisplayPort;
+    std::optional<std::string> mAssociatedDisplayUniqueId;
     std::optional<DisplayViewport> mAssociatedViewport;
     bool mHasMic;
     bool mDropUntilNextSync;