Write tests for other incremental generation Starlark integration

In order to get incremental generation mode into a proper build for additional widespread testing, I deferred some tests:

• Write compilation_providers tests
• Write compiler_args tests
• Write dependencies tests
• Write incremental_input_files tests
• Write incremental_library_targets tests
• Write incremental_output_files tests
• Write incremental_processed_targets tests
• Write incremental_resources tests
• Write incremental_top_level_targets tests
• Write incremental_unsupported_targets tests
• Write incremental_xcode_targets tests
• Write incremental_xcodeprojinfos tests
• Write products tests
• Write xcodeproj_incremental_aspect.bzl tests
• Write xcodeproj_incremental_rule.bzl tests

Start by locating the existing incremental generation Starlark integration tests and the entry points in xcodeproj_incremental_aspect.bzl and xcodeproj_incremental_rule.bzl. Add coverage for each unchecked integration area listed in the issue, including the compilation, dependency, input/output, target, product, and Xcode cases; done means all listed test items are implemented and passing.