Add context handling to Views blocks

Views blocks currently don't allow context to be passed in from a Layout. The only way to accomplish this now is to extract context from the URL based on position. This is less than ideal because it forces the block to be locked to a specific path structure that is separate from the Layout configuration.

Drupal 7 had the option to choose a data source "From context" in a View block. This code exists in Backdrop but has been commented out with a TODO. Perhaps this should be revisited to add context handling for Views blocks.

Update (April 3, 2023): The latest pull request for this issue adds context support to views blocks associated with layouts. There has been many revisions made to this pull request to address concerns from this wonderful Backdrop community. Some of these revisions have addressed improvements, efficiency changes, updated coding standards, etc. As of today, this PR has passed all the validation checks except one that seems to be some kind of external issue with that particular check.

Update (April 11, 2023): The latest pull request for this issue includes automated testing and is awaiting review. All validation tests have successfully passed.

Advocate for this feature: @rbargerhuff