Migrate to GR1CS

[alireza-shirzad]

Description

Updates r1cs-std to account for the changes in arkworks-rs/snark#378. This is mostly a renaming pass, but is a breaking-change.

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (master)
• Linked to Github issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Wrote unit tests
• Updated relevant documentation in the code
• Added a relevant changelog entry to the Pending section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

[Pratyush]

Please add a bash script which automates the migration.

[z-tech]

Could we fill in the description?

Is this purely a name change? And do we need or want this to be a breaking change?

[Pratyush]

@z-tech does the new description look good?

[z-tech]

Yes, it's clear. Thanks!