add phi nodes

[cqc-melf]

Description

This PR contains the second part of add phi nodes.

There are still 4 functions that needs to be removed to finish this.

Related issues

Please mention any github issues addressed by this PR.

Checklist

• [x] I have performed a self-review of my code.
• [x] I have commented hard-to-understand parts of my code.
• [x] I have made corresponding changes to the public API documentation.
• [x] I have added tests that prove my fix is effective or that my feature works.
• [x] I have updated the changelog with any user-facing changes.

[cqc-melf]

@cqc-alec Feel free to take a look at this now, I will add the last part in the next days. I will replace all the four functions for setting and getting bits from the i64 in the last step.

[cqc-melf]

I would like to merge this PR without adding the zext and trunc operations to have separate release candidates and make sure we can test this individually.