Consider enabling support in bmv2 backend for default_action in tables with action profiles or action selectors

[jafingerhut]

Since 2016, the p4c bmv2 backend has issued a warning if a table has a default_action property, and an implementation of an action profile or action selector. Then it produces a BMv2 JSON file that has no mention of the default_action at all. I believe this was done because at that time, BMv2 did not correctly implement those cases.

Since 2018, BMv2 should implement this correctly.

Links to commits/PRs with the 2016/2018 changes mentioned above can be found in the discussion thread following this comment: https://github.com/p4lang/behavioral-model/pull/1287/files#r1913623565

This issue is to track a possible enhancement to the p4c bmv2 backend that:
(a) no longer issues a warning for tables with a default_action property, if they have implementation that is action_profile or action_selector.
(b) for such tables, the BMv2 JSON data written for that table includes a description of the default_action of the table.

Of course, such a change should not be merged into p4c until after we have tested and verified that we believe BMv2 is working as expected for such tables.

[Vineet1101]

@jafingerhut I guess it can be solved. First we can remove warnings from backends/bmv2 files and then we can update the json generation. One thing that I would like to test is that does bmv2 handles the warning correctly