Adds support for the validation of IndexedSets using the index

[pmlpm1986]

Fixes #2655.

Summary/Motivation:

Set members could not be validated using the index in indexed sets. This PR adds that option to allow for more complex validation rules.

Changes proposed in this PR:

• Allows validation of indexed sets to access the member and the respective index just like in Parameter objects
• Supports one- and multi-dimensional set members
• Adds tests to retain the functionality
• Revised the tutorial to illustrate the functionality.

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[pmlpm1986]

I reverted the changes introduced by black. It should work as intended now.

[mrmundt]

I envision that future developers looking at this code will wonder, "What is I?"

[pmlpm1986]

In my mind, it is a simple set that we validate through the normal rule (no index).

[pmlpm1986]

That is, a non-indexed set.

[mrmundt]

I envision that future developers looking at this code will wonder, "What is J?"

[pmlpm1986]

In my mind, it is just an indexed set that we validate through this new rule.

[jsiirola]

This is pretty close. I really only have two concerns with it:

• I would prefer that this leverage the Initializer() logic if at all possible: that logic standardizes how we process arguments to Component constructors so that (hopefully) all Components / arguments behave the same.
• (and this is the bigger issue): this PR breaks backwards compatibility. That is, older models (including the tests in test_sets) no longer work with this change. Although The Book is ambiguous as to the signature that IndexedSet.validate should take, the fact that there are examples / tests that exercise the old convention makes me uneasy about breaking it. I think we should update this PR to either
  1. Work (silently) with either syntax
  2. Expect the new syntax but accept the old syntax (issuing a deprecation warning)

I am happy to work on a patch for this, but it will take me a little while to get to it.

[pmlpm1986]

This is pretty close. I really only have two concerns with it:

* I would prefer that this leverage the `Initializer()` logic if at all possible: that logic standardizes how we process arguments to Component constructors so that (hopefully) all Components / arguments behave the same.

* (and this is the bigger issue): this PR breaks backwards compatibility.  That is, older models (including the tests in `test_sets`) no longer work with this change.  Although The Book is ambiguous as to the signature that `IndexedSet.validate` should take, the fact that there are examples / tests that exercise the old convention makes me uneasy about breaking it.  I think we should update this PR to either
  
  1. Work (silently) with either syntax
  2. Expect the new syntax but accept the old syntax (issuing a deprecation warning)

I am happy to work on a patch for this, but it will take me a little while to get to it.

As you say, the book is vague about this and it led me to think Sets behaved exactly like Parameters. Once I realised that they did not, I raised this issue. Only recently did I find the time to come up with a solution. Therefore, the Initializer() approach makes sense but I never looked into it.

On the subject of backwards compatibility, the adjustments needed are minimal and by design: all that is needed is to add the index to the arguments (it is always the last argument) and ignore it, which is what I did in some of the tests. Issuing a deprecation warning seems reasonable.

[jsiirola]

This PR has been superseded by #3338 (that PR includes all commits here plus the rework of the Initializer and restoration of backwards compatibility [with deprecation warnings]). I am closing this PR to ease some of the burden on the CI system.