lcameraDev: add resolve-only deviceSelector API and deduplicate resolve paths.

Export lcameraDev_resolveDeviceSelectorCReq for attach-identity consumers,
factor live-camera snapshot helpers, and share resolveDeviceSelectorAgainstRecords
with get-or-create session acquisition.

Co-authored-by: Cursor <cursoragent@cursor.com>

commonLibs/lcameraDev/cameraManagerState.h

@@ -40,6 +40,9 @@ void lcameraDevExit();
 
 std::vector<std::shared_ptr<libcamera::Camera>> listLibcameraCameras();
 
+sscl::co::ViralNonPostingInvoker<CameraIdentityRecord>
+resolveDeviceSelectorCReq(const std::string& deviceSelector);
+
 sscl::co::ViralNonPostingInvoker<LcameraDevGetOrCreateResult>
 getOrCreateDeviceSessionCReq(const std::string& deviceSelector);