Support Symbolic Arrays of arbitrary length

[ven-k]

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Following is now supported:

@mtkmodel ModelWithArrays begin
    @structural_parameters begin
        N = 2
        M = 3
    end
    @parameters begin
        p1[1:4]
        p2[1:N]
        p3[1:N, 1:M] = 10, [description = "A multi-dimensional array of arbitrary length with description"]
        (p4[1:N, 1:M] = 10), [description = "An alternate syntax for p3 to match the syntax of vanilla parameters macro"]
    end
    @variables begin
        v1(t)[1:2] = 10, [description = "An array of variable `v1`"]
        v2(t)[1:3] = [1, 2, 3]
    end
end

A dedicated section, in the docs, describes it.

[ven-k]

The tests pertaining to Model-parsing (model_parsing and in dq_units and units)have passed. The failure looks unrelated.

[ven-k]

This PR is rebased off the master and NO_VALUE changes are included.

[ChrisRackauckas]

Missing the test using structural parameters

[ven-k]

Added here: 09de190#diff-3d89635366ad022b99bf84a74296abeb9423849838c8cfb8b5e8ede09f208c91R294-R313

[ChrisRackauckas]

is this one substantially more difficult to support?

[ven-k]

Not really.
Parser is now more granular. It picks up relevant bits of expression at the parsing step.
I've tried to batch similar ones together (example) and code is in a that is simpler to maintain.

Actually, let me add doc-strings to each parser step to indicate the syntax it parses.

[ven-k]

I have added the doc strings matching the block here: 4c0b1ed

[ven-k]

The doc failure is unrelated (errors stem from initialization.md)