Update some comments in test programs regarding recirculate, resubmit, and clone operations in v1model

[jfingerh]

At least these test programs have comments that will be obsolete after this PR is merged: #2902

v1model-special-ops-bmv2-first.p4

There may be more. It seems easier to wait until that other (large and complex) PR is merged, then fix up the comments in later commits.

This directory of example P4 programs is not part of any p4lang repo, but would also be good to update, at least to mark many of the programs there as of historical interest only, e.g. move them to an 'old-v1model-style' subdirectory, after PR #2902 is merged: https://github.com/jafingerhut/p4-guide/tree/master/v1model-special-ops

[jfingerh]

This documentation about v1model could also stand some updates after PR #2902 is merged: https://github.com/p4lang/behavioral-model/blob/main/docs/simple_switch.md

[jfingerh]

With these changes, there is no way to put the new @field_list annotation onto a field in any standard/intrinsic metadata structs. This seems like a reasonable restriction for this feature, and we should mention it in other documentation, including a suggested workaround that of course one is welcome to copy a standard metadata field value into a user-defined metadata field, and preserve the user-defined metadata field.

[jafingerhut]

This PR updates documentation of the v1model architecture in the p4lang/behavioral-model repo: p4lang/behavioral-model#1057

[jafingerhut]

This PR updates some comments in v1model.p4 include file and one of the p4c test programs that uses recirculate, resubmit, clone operations: #2985

[jafingerhut]

I have today updated multiples files in this directory of my p4-guide public repo related to recirculate/resubmit/clone and preserving user-defined metadata, too: https://github.com/jafingerhut/p4-guide/tree/master/v1model-special-ops

I am closing this issue. Feel free to open other issues if anyone finds obsolete documentation somewhere regarding these operations, on the repo containing that documentation.