Improve teams implementation

[vehre]

Improve the implemenation of team's functions to adhere to the Fortran 2018 standard and gfortran from 15 on.

coverage on master

Summary of changes

Summarize what you changed

Rationale for changes

OpenCoarrays was not implementing teams support correctly. This pull request adds the missing pieces and reworks non-standard complying parts. It also fixes the coarrays allocated in a teams block need to be freeed on exit issue.

Fixes #779 Fixes #545

Additional info and certifications

This pull request (PR) is a:

• [x] Bug fix
• [x] Feature addition
• [ ] Other, Please describe:

I certify that

• [x] I certify that:
  • I have reviewed and followed the contributing guidelines
  • I will wait at least 24 hours before self-approving the PR to give another OpenCoarrays developer a chance to review my proposed code
  • I have not introduced errant white space (no trailing white space or white space errors may be introduced)
  • I have added an explanation of what these changes do and why they should be included
  • I have checked to ensure there aren't other open Pull Requests for the same change
  • I have you written new tests for these changes
  • I have successfully tested these changes locally
  • I have commented any non-trivial, non-obvious code changes
  • The commits are logically atomic, self consistent and coherent
  • The commit messages follow best practices
  • Test coverage is maintained or increased after this is merged

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