audacity: update to 4.0.0, adopt; New package: Audacity3-3.7.9; pugixml: update to 1.15. - #62559

Testing the changes

• I tested the changes in this PR: YES
• Tested both on Pipewire by recording audio and playing it back
• Tested with both installed at the same time as well as only each one individually installed on its own.

New package

• This new package conforms to the package requirements: YES

Local build testing

• I built this PR locally for my native architecture, (x86_64)
• I built this PR locally for these architectures (if supported. mark crossbuilds):
  • x86_64-musl (doesn't build, but not the fault of this template - explained here.)
  • aarch64-musl
  • armv6l
  • armv7l
  • i686

Info about the PR

• Audacity 4 is basically a completely different app, both in terms of build system and on the user-end.
• Audacity 3 is still supported upstream through maintenance updates.
• Some people will still want to use Audacity 3, so I've opened a new package called audacity3 for that reason. This is identical to the live audacity package, just updated from 3.7.8 to 3.7.9, except for some post-install shenanigans to allow both packages to be installed at the same time. Audacity 4 should be reviewed as though it is a new package, even though it will be treated as an update by the package manager.
• Audacity 4 installs itself with the desktop name "Audacity 4 Portable", even if you build from source. Obviously we're not distributing the portable, so I amended the word " Portable" out of the desktop name.
• For consistency, I changed classic Audacity's desktop name from "Audacity" to "Audacity 3". You can see in the screenshot below what that looks like.
• I want both versions to be able to be installed together, so you will see some commands in post-install that will rename things from audacity to audacity3. I really do much prefer this to just saying the two packages conflict, since it's just stuff like binary names, desktop files, and desktop icons that need renaming. People may also want an easier way to compare the two programs, or have audacity classic as a backup while they learn the new audacity.
• Updating pugixml is probably not necessary, but Audacity 4 devs upstream tested it against the newer version, so it's safer to make sure pugixml is updated with Audacity.
• Comments should explain all the new patches for the most part.

Info for anyone who wants to review

• Make sure to pull the latest from the remote repo. Specifically, the qt6-6.11.2 update was merged a few days ago, and I encountered some errors before I realized I was behind on my packages.
• If this is your first time building qt6 with xbps-src, it might take a while to build. On my PC it took over an hour. After that, it builds in under 10 minutes for me. (Unless I was mistaken and that was just one time before I figured out the template properly.)
• No other package manager that I've seen has packaged Audacity 4 yet (not even flatpak or the AUR), so please do review!
• Do I need to worry about ardour3 showing up in the void updates page saying that it is available to be updated to v4? Is there a way to have it not show up there?

The amount of times I mistyped ardour instead of audacity drove me insane