[fdk-aac] make patent-encumbered HE-AAC optional (#16007)

* [fdk-aac] make patent-encumbered HE-AAC optional

By default, use a fork of fdk-aac (which was originally written
by Fraunhofer for the Android Open Source Project) which has
support for the patent-encumbered HE-AAC, HE-AACv2, and xHE-AAC
profiles removed. This fork is used by Fedora and Arch Linux to
provide support for most AAC use cases without patent licensing
fees and to permit combining it with GPL software. The upstream
fdk-aac with support for all AAC profiles can be built with the
new 'he-aac' option for this port.

Fedora Legal's opinion, from
https://bugzilla.redhat.com/show_bug.cgi?id=1501522#c112 :
The Fedora Project is aware that the Free Software Foundation
has stated that the Fraunhofer FDK AAC license is GPL
incompatible, specifically, because of Clause 3.

We believe that the fdk-aac software codec implementation that we
wish to include in Fedora is no longer encumbered by AAC patents.
This fact means that Clause 3 in the FDK AAC license is a "no op",
or to put it plainly, if no patents are in play, there are no
patent licenses to disclaim. For this (and only this) specific
implementation of fdk-aac, we believe that the FDK AAC license is
GPL compatible.

Also:
* remove restriction on dynamic linking. Upstream has a .def
file which is used by CMake.
* replace deprecated vcpkg functions

* [ffmpeg] use fdk-aac[he-aac] for fdk-aac feature

There is no point to this feature without HE-AAC because FFmpeg has
its own AAC codec that does not support HE-AAC.

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