DYN-8298: Fix python node script editor displays wrong script when closed as unsaved

[zeusongit]

Purpose

The following changes are made in the PR to fix the issue:

• The modified script is now provided using EventArgs instead of sender.
• The script returns to saved state, when a user closes the script editor without saving the changes.
• Added comments/cleanup

Declarations

Check these if you believe they are true

• The codebase is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning and are documented in the API Changes document.
• This PR modifies some build requirements and the readme is updated
• This PR contains no files larger than 50 MB

Release Notes

Fix python node script editor displays wrong script when closed as unsaved

Reviewers

@DynamoDS/dynamo

[github-actions]

See the ticket for this pull request: https://jira.autodesk.com/browse/DYN-8298