Fix tracking issues with the magnifier (#19483)
Fixes #19462
Summary of the issue:
Magnifier was not following focus properly according to @CyrilleB79 tests
Description of user facing changes:
Now using Focus Object/Navigator Object/Caret Position/Review Position to define what the magnifier should follow
Description of developer facing changes:
N/A
Description of development approach:
Creation of a Focus Manager that covers the proper objects
simplified Magnifier class
new specific tests
