Implement `insertVar` having `Identifier` parameter

[iambrj]

Currently, the insertVars for PresburgerSpace, IntegerRelation, and PresburgerRelation insert a null identifier for the new var. It would be convenient to have an insertVar which also takes an Identifier parameter.

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. In the comments of the issue, request for it to be assigned to you.
2. Fix the issue locally.
3. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
4. Create a Git commit.
5. Run git clang-format HEAD~1 to format your changes.
6. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Bharathi Ramana Joshi (iambrj)

Currently, the `insertVar`s for `PresburgerSpace`, `IntegerRelation`, and `PresburgerRelation` insert a null identifier for the new var. It would be convenient to have an `insertVar` which also takes an `Identifier` parameter.

[zjaffal]

I would like to take a look at this issue can you please assign it to me

[SahilPatidar]

@zjaffal are you still working on this?

[apoos-maximus]

If no progress has been made on this issue, and no one's working on it, I would love to start working on it ! @SahilPatidar