Add Dear ImPlot Library

Source/Core/DolphinLib.vcxproj

@@ -41,6 +41,7 @@
   <Import Project="$(ExternalsDir)FreeSurround\exports.props" />
   <Import Project="$(ExternalsDir)glslang\exports.props" />
   <Import Project="$(ExternalsDir)imgui\exports.props" />
+  <Import Project="$(ExternalsDir)implot\exports.props" />
   <Import Project="$(ExternalsDir)liblzma\exports.props" />
   <Import Project="$(ExternalsDir)libspng\exports.props" />
   <Import Project="$(ExternalsDir)libusb\exports.props" />