[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.

Author: jpobst

build-tools/jnienv-gen/Generator.cs

@@ -40,7 +40,7 @@ public static int Main (string [] args)
 
 try{
 using(TextWriterw=newStringWriter()){
-w.NewLine="\n";
+w.NewLine=Environment.NewLine;
 GenerateFile(w);
 stringcontent=w.ToString();
 if(jnienv_g_cs=="-")
@@ -50,7 +50,7 @@ public static int Main (string [] args)
 }
 using(TextWritersw=newStringWriter()){
 using(TextWriterhw=newStringWriter()){
-sw.NewLine="\n";
+sw.NewLine=Environment.NewLine;
 GenerateNativeLibSource(sw,hw,jnienv_g_h);
 stringsourceContent=sw.ToString();
 stringheaderContent=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}");
 }
 }