Perform all GTK interactions on the tray loop thread

[cgutman]

Description

GTK is not thread-safe, so we must only interact with GTK objects when running in our tray loop thread. However, it's not a simple as calling g_main_context_invoke() and returning, since many callers populate struct tray fields with variables located on the stack before calling tray_update(). To avoid those variables going out of scope, we block in tray_update() until the tray loop has processed our callback.

I tested the reproducer in LizardByte/Sunshine#1878 (comment) and was no longer able to reproduce the issue after applying this change.

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated