Preparation of Halogen-Containing 4 \textitH -Pyrido[ \textite ][1,3]oxazin-4-ones and Their Transformation into 2-Hydroxypyridinyl-Substituted 1,2,4-Oxadiazoles and 1,2,4-Triazoles: Halogen-Containing 4 \textitH -Pyrido[ \textite ][1,3]oxazin-4-ones