Synthesis, Structural, and UV Studies of Two Uracil Derivatives, Methyl 3-(5-Fluoro-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate and Methyl 3-(5-Chloro-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate