Fixed inconsistency in forwarding params in Context.forward

[Saif807380]

Context.forward uses Context.params to fill in the options and passes the kwargs to Context.invoke which creates a new Context for the sub-command but doesn't pass the params to the new Context nor does it remove unused kwargs.

From the example mentioned in the issue, now a union of params from the context and sub-context will be forwarded.

For e.g. - If command_1 has options a and b and command_2 has options a and c, command_1 forwards to command_2, then command_2 will receive a, b and c as kwargs.

I was unsure whether or not to remove the unused options, so I've kept them for now.

• fixes context.forward inconsistently removes undeclared options #1568

Checklist:

• Add tests that demonstrate the correct behaviour of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[davidism]

It seems a little weird to treat all kwargs as params, since params is supposed to hold the parsed values from @argument and @option. Another option is to separate into ctx.params and ctx.kwargs to track the decorated parameters vs everything the command was called with. I think it's fine as is for now, I'm not entirely sure the kwargs idea is any more "correct" in terms of the intentions of invoke, forward, and params.