Add support for bounding box image regions

[CPBridge]

There are specific templates for bounding boxes in structured reports. We should add support for these in highdicom. This would probably take the form of alternative "convenience" constructors for image regions, and search filters in the get_x_roi_measurement_groups() methods.

See @dclunie comment here for more context: https://github.com/QIICR/QuantitativeReporting/pull/287#discussion_r2128804492

Relevant links:

• CP 1852
• CID 219