Vectorization in the new Backend

Here, we track implementation progress of vectorization in the new pystencils backend.

The basic infrastructure and functionality is established with !424 (merged). The subtasks of this issue list the pending extensions to this, including a) rebuilding existing functionality from the legacy code generator, and b) new functionality that was not available in pystencils 1.3.x.

changed milestone to %Release 2.0

added feature label

added #105 as child task

added #106 as child task

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mentioned in task #84

added #108 (closed) as child task

mentioned in issue #46 (closed)

added #123 (closed) as child task

added #125 as child task