update barracuda version, enable tests for 2020.2 (#4571)

* update barracuda version, enable tests for 2020.2
* changelog
* variable backcompat version
* sync to tagged version of extensions

.yamato/test_versions.metafile

 # List of editor versions for standalone-build-test and its dependencies.
+# csharp_backcompat_version is used in training-int-tests to determine the
+# older package version to run the backwards compat tests against.
+    csharp_backcompat_version: 1.0.0
+    csharp_backcompat_version: 1.0.0
-# Waiting on a barracuda fix, see https://jira.unity3d.com/browse/MLA-1464
-#  - version: 2020.2
+    csharp_backcompat_version: 1.0.0
+  - version: 2020.2
+    # 2020.2 moved the AssetImporters namespace
+    # but we didn't handle this until 1.2.0
+    csharp_backcompat_version: 1.2.0

.yamato/training-int-tests.yml

     # If we make a breaking change to the communication protocol, these will need
     # to be disabled until the next release.
     - python -u -m ml-agents.tests.yamato.training_int_tests --python=0.16.0
-    - python -u -m ml-agents.tests.yamato.training_int_tests --csharp=1.0.0
+    - python -u -m ml-agents.tests.yamato.training_int_tests --csharp={{ editor.csharp_backcompat_version }}
   dependencies:
     - .yamato/standalone-build-test.yml#test_mac_standalone_{{ editor.version }}
   triggers:

com.unity.ml-agents/CHANGELOG.md

 
 ### Minor Changes
 #### com.unity.ml-agents (C#)
+- The Barracuda dependency was upgraded to 1.1.2 (#4571)
 #### ml-agents / ml-agents-envs / gym-unity (Python)
 
 ### Bug Fixes

com.unity.ml-agents/package.json

   "unity": "2018.4",
   "description": "Use state-of-the-art machine learning to create intelligent character behaviors in any Unity environment (games, robotics, film, etc.).",
   "dependencies": {
-    "com.unity.barracuda": "1.1.1-preview",
+    "com.unity.barracuda": "1.1.2-preview",
     "com.unity.modules.imageconversion": "1.0.0",
     "com.unity.modules.jsonserialize": "1.0.0",
     "com.unity.modules.physics": "1.0.0",

ml-agents/tests/yamato/yamato_utils.py

         return
 
     csharp_tag = f"com.unity.ml-agents_{csharp_version}"
-    csharp_dirs = ["com.unity.ml-agents", "Project"]
+    csharp_dirs = ["com.unity.ml-agents", "com.unity.ml-agents.extensions", "Project"]
-        subprocess.check_call(f"git checkout {csharp_tag} -- {csharp_dir}", shell=True)
+        # Allow the checkout to fail, since the extensions folder isn't availabe in 1.0.0
+        subprocess.call(f"git checkout {csharp_tag} -- {csharp_dir}", shell=True)
 
 
 def undo_git_checkout():