Fixes an issue introduced in 72fa2d98e1
where zeromem might write past the end of the channel buffer.

If the block size changes from block to block, then it's possible for
inputBuffer to be smaller than buffer, but for buffer to be smaller than
the initially-allocated size of inputBuffer.

We haven't updated the default post-build copy paths yet, as the new
local directory is not yet well-supported by DAWs.

When plugins change their 'parameter info' this often means that their
previous parameter text is no longer valid, so we should fetch new text
to represent the parameter value.

This change was primarily tested with Kontakt.

This change was tested with FabFilter Pro Q 3, which supports new AU
channel layouts for Atmos.

With this patch applied, the DemoRunner should build under MinGW, and be
(nearly) feature-complete compared to the MSVC build.

Specifically, when building with MinGW:
- Adds support for accessibility
- Fixes build issues in the juce_video module
- Fixes a link issue in the VST3 wrapper when VST3_CAN_REPLACE_VST2 is
  defined
- Adds support for the new-style native FileChooser
- Tidies up some other low-severity warnings

Known issues:
- Direct2D rendering is still not supported when building with MinGW due
  to ABI compatibilities.

Previously, right-clicking on a slider could change its value, but the
parameter value would not be changed, leaving the slider in a different
state to the parameter.

When opening the "settings" menu of Arturia Pigments VST2, the editor
window would move itself over the JUCE non-native titlebar in the
AudioPluginHost. Then, when the editor was moved back into the correct
location, the titlebar would not be redrawn, leaving it in an incorrect
state.

This change forces a repaint of the editor's peer whenever the size
changes, forcing the titlebar to repaint after the editor has moved.

This fixes an issue where the editor of VocAlign Project 5 would fail to
open in the AudioPluginHost.

Fixes a bug introduced in 7d1918b385c600e1910dd5b744b583a42a26d8a1,
where Ozone 9's editor failed to open correctly in the AudioPluginHost.

Native Instrument VST3s (I tested Kontakt and Supercharger) crash when
the bundleEntry function is called from a background thread on macOS.
This change disables scanning for VST3 plugins on a background thread
using the PluginListComponent, to allow loading these plugins in the
AudioPluginHost.

I can't find any "official" word on whether the bundleEntry and
bundleExit functions should be guaranteed to be made from the main
thread. However, the VST3PluginTestHost app seems to call these
functions exclusively from the main thread.