[MacPorts] #48192: libass: update to 0.12.2, port to GitHub

[MacPorts]

#48192: libass: update to 0.12.2, port to GitHub
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 Reporter:  ionic@…   |      Owner:  coax@…
     Type:  update    |     Status:  new
 Priority:  Normal    |  Milestone:
Component:  ports     |    Version:
 Keywords:  haspatch  |       Port:  libass
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 `libass` has seen newer versions for a while, but the port is currently
 stale at version 0.10.2.

 Furthermore, the project switched to GitHub some time ago.

 It is `openmaintainer`, but due to the changed being quite substantial,
 I'm not committing without asking the maintainer first.

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Ticket URL: <https://trac.macports.org/ticket/48192>
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