UI: Stop locking filter mutex while loading properties

[exeldro]

Description

Reordering the filters makes the filter mutex of the source locked while loading a new the properties of a filter which may require other locks. By loading the properties of the filter on a QueuedConnection we make sure the filter mutex is cleared when that happens.

Motivation and Context

I don't like deadlocks.
The main UI thread gets a lock on the filter mutex followed by a lock on the app sources mutex to fill the properties of the filter
while the graphics thread does a lock on the app sources mutex followed by a lock on the filter mutex

How Has This Been Tested?

On windows 64 bit by reordering move transition override filters

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[WizardCM]

Is this a new issue in the beta, or slightly more longer-standing?