Issue #8127: Option to load reduced TIFFs

Merged Alx Sa requested to merge alxsa/tiff-reducedimage-option-2.99 into master

This patch ports the in-progress changes from !656 (merged) to 2.99, since there's no longer a rush for inclusion in 2.10.32 and it will probably be more convenient for reviewers to test. If approved, !656 (merged) will be updated with the final code. All current review comments from !656 (merged) have been implemented in this code.

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