Apply #pragma once, misc cleanup (#12322)

* Apply #pragma once in headers
* Adjust some thermistors formatting
* Misc cleanup and formatting

Marlin/src/feature/I2CPositionEncoder.h

@@ -19,9 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
-
-#ifndef I2CPOSENC_H
-#define I2CPOSENC_H
+#pragma once
 
 #include "../inc/MarlinConfig.h"
 
@@ -331,5 +329,3 @@ class I2CPositionEncodersMgr {
 };
 
 extern I2CPositionEncodersMgr I2CPEM;
-
-#endif //I2CPOSENC_H