Comments for parser denylist

[Abdurrahheem]

Relates to https://github.com/opencv/opencv/issues/21078

This PR is designed to figure out why the test in test_onnx_conformance_layer_parser_denylist.inl.hpp fails. Currently, conformance tests do not pass for the following reasons:

1. BOOL, INT(8, 16) types are not supported (MAJOR)
2. Some layers can not be created due to various reasons (MAJOR)
3. Shape mismatches while creating layers (MAJOR)
4. Some layers are expected to support dynamic parameter initialization (MAJOR)
5. Some layers are expected to receive weight as inputs (no idea why that is needed) (MAJOR)

6. Other unknown reasons

   (MAJOR) - These are the most frequently encountered reasons for test failure.

   The style of comments is not consistent everywhere. Let's keep this PR without merging, just for our reference. A couple of tests are commented on since they have passed on the MacOS platform.

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[fengyuentau]

Some layers are expected to receive weight as inputs (no idea why that is needed) (MAJOR)

Most probably they need to be trainable. But we do not need to take care of this "trainable" feature.