[Xamarin.Android.Build.Tasks] no temp files in GenerateJavaStubs

[jonathanpeppers]

Context: #2505

This is based on #2505, but I incorporated the java.interop changes so
GenerateJavaStubs uses no temp files at all.

In many places throughout the Xamarin.Android build, we have a pattern
of:

• Generate a temp file.
• Use MonoAndroidHelper.CopyIfChanged to put the file in the
  destination. This reads both files, doing a hash comparison before
  deciding to write or not.
• Delete the temp file.

Sometimes the temp file is actually in %TEMP%, but other times we
append .new to the destination file. The case of .new can collide
if two builds are running at once (example caused by a known VS for
Mac issue).

Thinking about this, in cases with small files, we can make a simple
optimization:

• Generate the file in-memory.
• Use a new MonoAndroidHelper.CopyStreamIfChanged method`.

This has several benefits:

• We never write a file to disk when there are no changes.
• We don't have to remember to delete the file.
• The code, in general, is slightly simpler.

The only place we likely shouldn't use this new pattern, would be if
the file was huge.

Changes

I added new APIs for:

• Files.HasStreamChanged - to compare a Stream in memory
• Files.HasBytesChanged - to compare a byte[] in memory
• Files.CopyIfStreamChanged
• Files.CopyIfStringChanged - some cases we have a string
• Files.CopyIfBytesChanged - this supports string
• MonoAndroidHelper.CopyIfStreamChanged
• MonoAndroidHelper.CopyIfStringChanged
• MonoAndroidHelper.CopyIfBytesChanged

I changed the following MSBuild tasks, mostly to test out the new
behavior:

• GenerateResourceDesigner was using a .new file.
• GenerateJavaStubs was using temp files in many places. I was able
  to fix up all of these.
• ManifestDocument now has an overload for Save that takes a
  Stream
• Generator now uses CopyIfStreamChanged a new
  GetDestinationPath method from java.interop. It reuses a single
  MemoryStream, and I moved the GenerateJavaSource method into
  CreateJavaSources for simplicity.

I made other general refactoring in GenerateJavaStubs:

• Since we don't have to worry about deleting a temp_map_file, we
  can return earlier if Generator.CreateJavaSources fails.
• A GetResource<T> method, cleans up the places reading from
  EmbeddedResource files. I also changed it up to properly Dispose
  things.
• A save anonymous method/delegate should just be a SaveResource
  regular method.
• A few places were calling Path.GetFullPath unecessarily. Since
  this method accesses the file system, we should skip it unless the
  full path is actually needed.
• Avoid using StringWriter and string.Format.
• Use capacity and StringComparer.Ordinal when creating
  dictionaries: https://www.dotnetperls.com/dictionary-stringcomparer
• Preallocate MemoryStream with java_types.Length * 32

I also added some tests for the new APIs in MonoAndroidHelper.

Results

I did three test runs, because I was getting varying times for
GenerateJavaStubs. This is the Xamarin.Forms integration project in
this repo:

Before (Clean Build):
1. 1433 ms  GenerateJavaStubs                          1 calls
2. 1594 ms  GenerateJavaStubs                          1 calls
3. 1353 ms  GenerateJavaStubs                          1 calls

After (Clean Build):
1. 1201 ms  GenerateJavaStubs                          1 calls
2. 1137 ms  GenerateJavaStubs                          1 calls
3. 1136 ms  GenerateJavaStubs                          1 calls

Before (Incremental):
1. 1184 ms  GenerateJavaStubs                          1 calls
2. 1181 ms  GenerateJavaStubs                          1 calls
3. 1172 ms  GenerateJavaStubs                          1 calls

After (Incremental):
1. 1035 ms  GenerateJavaStubs                          1 calls
2. 1049 ms  GenerateJavaStubs                          1 calls
3. 1036 ms  GenerateJavaStubs                          1 calls

GenerateJavaStubs is now about 250ms faster on initial build and
150ms faster on incremental builds.

I could not see a difference in GenerateResourceDesigner, likely
since it wrote only a single temp file.

Next steps would be to make changes in other MSBuild tasks as well.

[jonathanpeppers]

Logs from third run: logs.zip

[jonathanpeppers]

build

[jonathanpeppers]

The test failure just seems to say this from the build log:

/Users/builder/jenkins/workspace/xamarin-android-pr-builder-release/xamarin-android/build-tools/scripts/TestApks.targets(189,5):
   Process '/Users/builder/android-toolchain/sdk/platform-tools/adb -s emulator-5570  shell am instrument  -e "loglevel Verbose" -w "Xamarin.Android.Bcl_Tests/xamarin.android.bcltests.NUnitInstrumentation"' failed to exit within the timeout of 1800000ms, killing the process [/Users/builder/jenkins/workspace/xamarin-android-pr-builder-release/xamarin-android/tests/RunApkTests.targets]

I'm going to retry it.