[class-parse] Use BufferedStream to increase performance (#1092)

While building `AndroidX.sln`, `class-parse` is taking up a
considerable amount of time.  After some quick profiling, this seems
to be caused by reading from a `ZipStream` one or two bytes at a time.
Wrapping the `ZipStream` in a `BufferedStream` makes `class-parse`
about 10x faster on larger test cases.

|                                                                 |  0d5cddb |       Now |
| --------------------------------------------------------------- | --------: | --------: |
| `class-parse` on API-33 `android.jar` (26.5 MB)                 |   16.675s |    2.759s |
| `class-parse` on `androidx.compose.runtime.runtime` (1.044 MB)  |    9.713s |     .893s |
| Total `class-parse` time building `AndroidX.sln`                |  5:48.46m |  2:09.73m |
| Total time building `AndroidX.sln`                              |  7:40.19m |  4:42.34m |

Author: jpobst

src/Xamarin.Android.Tools.Bytecode/ClassPath.cs

@@ -72,7 +72,8 @@ public void Load (Stream jarStream, bool leaveOpen = false)
 						if (!ClassFile.IsClassFile (s) || entry.Name.EndsWith (".jnilib", StringComparison.OrdinalIgnoreCase))
 							continue;
 					}
-					using (var s = entry.Open ()) {
+					using (var entry_stream = entry.Open ())
+					using (var s = new BufferedStream (entry_stream)) {
 						try {
 							var c   = new ClassFile (s);
 							Add (c);