This is mostly a simple lexical search+replace but the absence of operator< for
std::weak_ptr<T> leads to some complications, particularly with Evoral::Sequence
and ExportPortChannel.
* Allow to bundle presets
* Do not use /usr/[local] on Windows
(This may need further work, for Windows, since default user
presets are in `file://$HOME/.ladspa/rdf/`)
Plugins on Apple can be multi-arch (Intel + ARM), or AUs may
be bridged by Rosetta.
A user can also run Intel binary of Ardour or M1 binary on
M1 CPUs on macOS. Each can see different plugins - notably
VST3 plugins that are Intel only can be scanned using the
Intel binary, but are later not available with the M1 build.
ARDOUR::SystemExec is also used for scanning VST2 and AU plugins, yet
the corresponding header ardour/system_exec.h is not included when VST3
support is disabled in the build configuration.
Ardour prevents repeat crashes by first marking a plugin
as blacklisted, and after a successful scan the plugin is
whitelisted.
When not scanning for plugins, but reading the cache
and successfully parsing the cashed content, a VST2 plugin
is whitelisted, even though it may not have been blacklisted.
In case the blacklist is empty, this lead to a logging:
"Expected VST Blacklist file does not exist."
PS. This also consolidates VST2 + VST3 code for white/blacklist
This happens with e.g. the IEM suite when a user has both
/usr/lib/vst and /usr/lib/lxvst in the search path.
The same plugin was found twice due to symlinks:
```
/usr/lib/lxvst/iem.at -> ../x86_64-linux-gnu/iem-plugin-suite/vst
/usr/lib/vst/iem.at -> ../x86_64-linux-gnu/iem-plugin-suite/vst
```
And then blacklisted itself:
> "Ignoring plugin 'MultiBandCompressor'.
> VST-ID conflicts with other plugin 'MultiBandCompressor' files:
> '/usr/lib/x86_64-linux-gnu/iem-plugin-suite/vst/MultiBandCompressor.so' vs
> '/usr/lib/x86_64-linux-gnu/iem-plugin-suite/vst/MultiBandCompressor.so'
Particularly on macOS child process ReadStdout
may produce many partial lines unbuffered lines.
Since each log message appends a newline, the log
had entries like:
```
Thi
s is a
n examp
le
```
This is only relevant when manually scanning plugins,
initiated from the UI thread. Call back (in same thread) needs
to happen after detecting ambiguities and refilling the info lists.
