Revise the implementation with getting the default file path. Now it works with primary delay.

[yelmuratoff]

Describe the bug
Revise the implementation with getting the default file path. Now it works with primary delay.
At the moment, since the tests themselves are run in a temporary directory, so, we cannot use Platform.script to get access to the path of the running script we have to make numerous checks through the dcli library. Because of this, there is some delay at the beginning of the test launch.

To Reproduce
Steps to reproduce the behavior:
You can just use any method without specifying a file path.

Expected behavior
We need the standard path to be much faster than it would be in a normal environment, not a test environment.

It doesn't matter what device you test in. But I tested it on macOS and Windows.

For the original problem, there are already existing issues in the main repositories:

• Platform.script should return a meaningful directory in tests. flutter/flutter#137638
• Add the ability to get the current script or project path when using the new test runner dart-lang/test#110

[yelmuratoff]

Started to fix this problem without using third-party libraries.
Issue branch: https://github.com/approvals/ApprovalTests.Dart/tree/fix/script_path_issue