Add ClearBreakpoints API

Add a test which actually triggers the mappings and fires up vimspector
with the cpptools debugger.

tests/testdata/cpp/simple/simple.cpp

@@ -0,0 +1,18 @@
+#include <iostream>
+
+namespace
+{
+  void foo( int bar )
+  {
+    int unused;
+
+    printf( "%d\n", bar );
+  }
+}
+
+int main( int argc, char ** )
+{
+  printf( "this is a test %d\n", argc );
+  foo( argc );
+  return 0;
+}