[SRU] Carla can't find plugins in plugin directories located in the user's home

[Impact]

Users of Carla are unable to refresh audio plugins when more are installed, i.e. in the user's home directory. Furthermore, this can cause Carla to crash.

[Test Plan]

 * Launch Carla
 * Click "Add Plugin"
 * Click "Refresh"
 * Click "Scan"

 Expected: Carla will scan for new plugins and find them.

 Actual: Carla does not scan for plugins, and may crash.

[Where problems could occur]

 * This may simply cause a regression in Carla in which save files may cease to load or other issues with plugins loading, however this is highly unlikely.

[Other Info]

Originally the plan for this SRU was to upload a patched version of Carla 2.4.2 which did not work as planned. 2.4.3 FTBFS when uploaded to Kinetic, as did 2.4.4 when uploaded to a PPA built against Kinetic. Eventually, it was proven that 2.4.4 would build cleanly in Jammy and introduces essential bugfixes, including this fix as well as fixes Python 3.10 compatibility issues that were merely patched before.

It is to be noted that this upstream version does *NOT* introduce any new features, and the upstream developer was aware that any fixes he made in this release could not introduce new features and could only introduce bugfixes. As stated from the changelog, these bugfixes, including the one in this SRU, include:

 * Fix inaccurate MIDI CC rounding
 * Fix python3.10 compatibility issues
 * Fix integration with internal Qt toolbar visibility state

From a usability standpoint, these are essential fixes in functionality.

It is also to be noted that the upstream developer primarily develops on focal for focal and bionic and was unaware of the primary issue until it was brought to his attention, but could not work it until he had a docker image of jammy in a stable release. It was at that point he discovered the other issues.

For that reason, I do apologize for the large diff, and I hope this is a good explanation for that and the bugs fixes covered in the diff. Rather than filing separate bug reports for each of these, I'd rather get it all taken care of with at once here.

- Erich Eickmeyer

Original bug report as follows:
------

In the LV2 location in my home directory .lv2 I have the following plugin:

➜ ls ~/.lv2
librnnoise_lv2.so

${HOME}/.lv2 is configured in Carla as a search path.

In the Add Plugin dialog for Carla if I search for noise nothing shows up.

This worked fine previously on 21.10.

Release notes for Carla 2.4.3 [1] include this line: Fix plugin search (regression from 2.4.2)

Ubuntu Studio 22.04 currently has the bugged version:

➜ carla --version
Using Carla version 2.4.2

[1] https://github.com/falkTX/Carla/releases/tag/v2.4.3

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: carla 2.4.2-0ubuntu2
ProcVersionSignature: Ubuntu 5.15.0-24.24-lowlatency 5.15.30
Uname: Linux 5.15.0-24-lowlatency x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu82
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Thu Apr 21 15:41:13 2022
InstallationDate: Installed on 2022-04-20 (1 days ago)
InstallationMedia: Ubuntu-Studio 22.04 LTS "Jammy Jellyfish" - Beta amd64 (20220329.1)
SourcePackage: carla
UpgradeStatus: No upgrade log present (probably fresh install)