matrix: provide 'matrix' eval context when decoding the matrix

[ryancragun]

When decoding matrix blocks we'll now expose a matrix eval context which contains values from previously evaluated attributes. This allows us more flexibility when constructing values for include or exclude blocks.

• Create and update the 'matrix' key in the eval context when decoding matrix blocks.
• Update existing valid matrix decode test to use an expression that refers to previously defined key.
• Fix deprecation warning in linter.
• Bump version

This allows us to do cool things like this:

Checklist

• The commit message includes an explanation of the changes
• Manual validation of the changes have been performed (if possible)
• New or modified code has requisite test coverage (if possible)
• I have performed a self-review of the changes
• I have made necessary changes and/or pull requests for documentation
• I have written useful comments in the code