Update Figlet implementation to be PHP8 compatible

Summary:
As of PHP ~v8 the zip_open and associated functions have been deprecated and
removed. The replacement is the ZipArchive API. This updates the figlet
implementation to use this API which has been present in PHP since 5.2.

Additionally in PHP 8 the use of squiggly brackets for indexing into arrays is
also deprecated. This updates to remove two uses of squiggly brackets and
replace with square brackets.

These two deprecations would result in being unable to load differential
revisions in which someone had commented using figlet remarkup.

Refs T13588

Test Plan:
Applied these changes to an install and loaded a revision that had comments
where someone utilized figlet remarkup. The revision loaded properly and the
figlet comment rendered properly.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin

Maniphest Tasks: T13588

Differential Revision: https://secure.phabricator.com/D21860