Stage initial set of changes for the Catapult backend

[dgburnette]

A# Description This is the initial merge of a Catapult backend for HLS4ML. This merge includes all of the python changes and the top-level template files but not the nnet_utils/* files at this point in time.

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Type of change

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• [ ] Bug fix (non-breaking change that fixes an issue)
• [ ] Documentation update
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] A new research paper code implementation
• [ ] Other (Specify)

Tests

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Test Configuration:

Checklist

• [x] I have read the guidelines for contributing.
• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] I have made corresponding changes to the documentation.
• [ ] My changes generate no new warnings.
• [ ] I have installed and run pre-commit on the files I edited or added.
• [ ] I have added tests that prove my fix is effective or that my feature works.

[jmitrevs]

Based on our meeting, we have the following action items:

1. In backends/catapult/passes, remove any passes that are not used.
2. Also in backends/catapult/passes, note passes that are used but identical with what is used for Vivado. We will figure out how we want to handle those.
3. Remove any build scripts or parts of build scripts that are not used. Remove references to Vivado.
4. Put ac_types and other submodules in hls4ml/template/cataplult. (I think you can just do git submodule add in that directory)
5. Add migrated nnet_utils to the template/catapult/nnet_utils. This includes some common utils and layer-specific utils. Do not include untested layers.
6. All the layers that are included in nnet_utils should have corresponding tests in test/pytest. Generally this could be done by just enabling the catapult backend on already existing tests instead of writing new tests.