Deduplicate test code

Remove duplicated coverall test code from `compatibility-test/tests`.
Write a script to download these tests from their respective
repositories straight into `compatibility-tests/tmp` directory.

Split up `test_generators.sh` into multiple files, because the file
was becoming unmaintainable.

Signed-off-by: Kristupas Antanavicius <[email protected]>

Author: arg0d

.github/workflows/tests.yml

@@ -37,8 +37,8 @@ jobs:
         with:
           name: test-libs
           path: |
-            target/debug/libuniffi_coverall.so
-            target/debug/libuniffi_coverall.a
+            target/debug/libcompatibility_test.so
+            target/debug/libcompatibility_test.a
 
   test:
     runs-on: ubuntu-latest