This patch updates the Font Awesome library version from 4.7 to 6.3.0.
The readme_moodle.txt has been updated properly because the new version
works slightly different.
There is a file to add backward compatibily to version 6 files (shim).
More information about how to upgrade from 4 to 6 can be found in
https://fontawesome.com/docs/web/setup/upgrade/upgrade-from-v4
Although a few icons have been renamed in Moodle 6, as the new version
is compatible with v4 icons, for now the references to the old icons
(fa fa-xxxx --> fa-solid fa-xxxx) haven't been changed yet.
A separate issue will be created to update them in the future and
review if some new icons can be used too.
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