Fixes #4332 - Refactor test infrastructure to use modern ApplicationImpl.Coordinator instead of legacy MainLoop (#4335)

* Initial plan

* Refactor tests to use modern ApplicationImpl.Coordinator architecture instead of legacy Application.RunIteration

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Changes before error encountered

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Replace Application.RunIteration implementation to use modern ApplicationImpl.Coordinator architecture

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Simplify Application.RunIteration to directly delegate to ApplicationImpl.Coordinator without legacy infrastructure

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Update multitasking.md documentation to use Application.AddTimeout/RemoveTimeout instead of deprecated Application.MainLoop methods

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Refactor contribution guidelines and documentation

- Consolidated all contribution-related instructions into `CONTRIBUTING.md` as the single source of truth.
- Updated `copilot-instructions.md` and `AGENTS.md` to reference `CONTRIBUTING.md`.
- Enhanced build, test, and CI/CD workflow documentation.
- Updated repository structure documentation in `README.md` and `CONTRIBUTING.md`.
- Reinforced coding conventions and streamlined testing requirements.
- Documented GitHub Actions workflows and provided local CI replication steps.
- Refined API documentation requirements and PR guidelines.
- Simplified `.sln` file and removed redundant content.
- Updated links to point to the latest documentation resources.

* Revamp bug report template for clarity and detail

Updated the bug report template to improve structure, readability, and comprehensiveness:
- Specified "Terminal.Gui" in the `about` section.
- Replaced bold headings with Markdown heading syntax.
- Enhanced "To Reproduce" with placeholders for code and behavior details.
- Added an "Environment" section to collect OS, terminal, PowerShell, .NET, and `Terminal.Gui` version details.
- Expanded "Screenshots" to include GIFs and terminal output instructions.
- Removed outdated "Desktop" and "Smartphone" sections, consolidating relevant details.
- Improved "Additional Context" with prompts for consistency, prior behavior, and error messages.
- Streamlined "For Maintainers" instructions for setting project and milestone.

These changes aim to make bug reports more actionable and easier to reproduce.

* Remove [Obsolete] attribute and pragma warnings from Application.RunIteration - method now uses modern architecture internally

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Refactor Application.Run.cs for clarity and cleanup

Removed debug assertions and unused/commented-out code to simplify logic and improve maintainability. Renamed `forceDraw` to `forceRedraw` in `LayoutAndDraw` for better clarity. Removed the internal `OnNotifyStopRunState` method and its associated logic, indicating a refactor of the stop notification mechanism.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Tig <tig@users.noreply.github.com>
Co-authored-by: tig <585482+tig@users.noreply.github.com>

docfx/docs/multitasking.md

@@ -89,7 +89,7 @@ public class ClockView : View
         Add(timeLabel);
         
         // Update every second
-        timerToken = Application.MainLoop.AddTimeout(
+        timerToken = Application.AddTimeout(
             TimeSpan.FromSeconds(1), 
             UpdateTime
         );
@@ -105,7 +105,7 @@ public class ClockView : View
     {
         if (disposing && timerToken != null)
         {
-            Application.MainLoop.RemoveTimeout(timerToken);
+            Application.RemoveTimeout(timerToken);
         }
         base.Dispose(disposing);
     }
@@ -220,7 +220,7 @@ Task.Run(() =>
 ### ❌ Don't: Forget to clean up timers
 ```csharp
 // Memory leak - timer keeps running after view is disposed
-Application.MainLoop.AddTimeout(TimeSpan.FromSeconds(1), UpdateStatus);
+Application.AddTimeout(TimeSpan.FromSeconds(1), UpdateStatus);
 ```
 
 ### ✅ Do: Remove timers in Dispose
@@ -229,7 +229,7 @@ protected override void Dispose(bool disposing)
 {
     if (disposing && timerToken != null)
     {
-        Application.MainLoop.RemoveTimeout(timerToken);
+        Application.RemoveTimeout(timerToken);
     }
     base.Dispose(disposing);
 }