[invocation-overhead] Add generated source files (#1175)

Building the `Java.Interop.sln` solution always produces some generated
files that `git` wants to try to commit:

	Changes not staged for commit:
	  (use "git add <file>..." to update what will be committed)
	  (use "git restore <file>..." to discard changes in working directory)
	        modified:   tests/invocation-overhead/jni.cs

	Untracked files:
	  (use "git add <file>..." to include in what will be committed)
	        tests/invocation-overhead/jni-api.h
	        tests/invocation-overhead/jni.c

Commit these generated files, and update the generator for `jni.cs` to
always use native platform new lines so it does not show up as modified
on Windows.

build-tools/jnienv-gen/Generator.cs

@@ -40,7 +40,7 @@ public static int Main (string [] args)
 
  try {
  using (TextWriter w = new StringWriter ()) {
- w.NewLine = "\n";
+ w.NewLine = Environment.NewLine;
  GenerateFile (w);
  string content = w.ToString ();
  if (jnienv_g_cs == "-")
@@ -50,7 +50,7 @@ public static int Main (string [] args)
  }
  using (TextWriter sw = new StringWriter ()) {
  using (TextWriter hw = new StringWriter ()) {
- sw.NewLine = "\n";
+ sw.NewLine = Environment.NewLine;
  GenerateNativeLibSource (sw, hw, jnienv_g_h);
  string sourceContent = sw.ToString ();
  string headerContent = hw.ToString ();
@@ -254,13 +254,13 @@ static void GenerateJniNativeInterfaceInvoker (TextWriter o, HandleStyle style)
  continue;
  o.WriteLine ();
  if (e.Prebind)
- o.WriteLine ("\t\tpublic readonly {0} {1};\n", d, e.Name);
+ o.WriteLine ("\t\tpublic readonly {0} {1};{2}", d, e.Name, Environment.NewLine);
  else {
  o.WriteLine ("\t\t{0}? _{1};", d, e.Name);
  o.WriteLine ("\t\tpublic {0} {1} {{", d, e.Name);
  o.WriteLine ("\t\t\tget {");
- o.WriteLine ("\t\t\t\tif (_{0} == null)\n\t\t\t\t\t{1}", e.Name, Initialize (e, "_", d));
- o.WriteLine ("\t\t\t\treturn _{0};\n\t\t\t}}", e.Name);
+ o.WriteLine ("\t\t\t\tif (_{0} == null){2}\t\t\t\t\t{1}", e.Name, Initialize (e, "_", d), Environment.NewLine);
+ o.WriteLine ("\t\t\t\treturn _{0};{1}\t\t\t}}", e.Name, Environment.NewLine);
  o.WriteLine ("\t\t}");
  }
  }