[wpilib] Use reflection to load main class, remove main from templates (#8627)

#8626 needs to switch to using reflection to load the robot class. Do
that with this PR so it's separate.

Also, remove the duplicated main files from the template, and instead
fixup vscode to handle this properly.

wpilibcExamples/src/main/cpp/examples/examples.json

@@ -520,7 +520,6 @@
     ],
     "foldername": "Xrptimed",
     "gradlebase": "cppxrp",
-    "mainclass": "Main",
     "commandversion": 2,
     "extravendordeps": [
       "xrp"