Add cross-platform GDB debugger with C++ support

[Copilot]

The OneWare.Debugger module had partial GDB MI code but was never wired up — the view shipped as a "Coming Soon!" placeholder and BreakpointStore had its debugger hooks commented out. This PR completes it into a working, cross-platform GDB debugger usable against C++ projects.

OneWare.Debugger

• GdbSession becomes a concrete (non-abstract) class; RunCommand / RunCommandAsync are now public and a thread-safe IsRunning is exposed.
• New IDebuggerService / DebuggerService (DI singleton) owns at most one active session, applies the shared breakpoints, forwards GDB output to IOutputService, and exposes StartAsync / Stop / Continue / Pause / Step / Next / Finish. Breakpoints toggled while a session is live are applied/removed automatically. Async MI mode is used everywhere except Windows (which falls back to the existing SIGINT helper for pause).
• DebuggerModule registers the service, eagerly resolves it at startup so it observes the breakpoint store, and registers a Tools/Debugger/GDB Path FilePathSetting with OS-specific defaults (gdb.exe on Windows, gdb elsewhere) and PATH-based auto-detection at start time.
• DebuggerViewModel / DebuggerView replace the placeholder with a functional toolbar (Start/Stop/Continue/Pause/Step/Next/Finish) and an executable picker, bound to IsDebugging / IsRunning for CanExecute.

OneWare.Essentials

• BreakpointStore exposes a single shared Instance, and ExtendedTextEditor.SetEnableBreakpoints binds every editor margin to it. The previous per-margin store made cross-file debugging impossible — only breakpoints in the editor that started the session were observable. C++ already has CanAddBreakPoints => true, so C++ breakpoints now flow into the live GDB session without further wiring.

// Start a GDB session for any ELF / EXE; breakpoints from every open editor are applied.
var debugger = serviceProvider.Resolve<IDebuggerService>();
await debugger.StartAsync("/path/to/main");
debugger.Continue();

Tests

• New tests/OneWare.Debugger.UnitTests/ with 6 tests for GDB MI output parsing: GdbCommandResult (^done with nested results, ^error,msg=..., ^running, ^connected) and GdbEvent (*stopped at a breakpoint with frame / fullname / line, *running).

Notes / follow-ups

• _exec-run is used to launch the inferior with a fallback to _exec-continue; remote-target / attach flows are not yet exposed.
• Settings UI lets users override the GDB path; Windows users debugging C++ should point this at their toolchain's gdb.exe (e.g. MSYS2 / MinGW) since one isn't auto-installed.
• macOS ships lldb rather than gdb by default — users will need to install gdb (brew install gdb, code-sign) or we follow up with an lldb-mi backend behind the same IDebuggerService.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• www.myget.org
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.25.1/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp /opt/hostedtoolcache/CodeQL/2.25.1/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp (dns block)
  • Triggering command: /usr/share/dotnet/dotnet dotnet restore --no-dependencies /home/REDACTED/work/OneWare/OneWare/src/VtNetCore.Avalonia/VtNetCore.Avalonia.sln --packages /tmp/codeql-scratch-4731918ca57aa503/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/tmp/codeql-scratch-4731918ca57aa503/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/tmp/codeql-scratch-4731918ca57aa503/dbs/csharp/working/emptyFakeDotnetRoot /p:AllowMissingPrunePackageData=true (dns block)
  • Triggering command: /usr/share/dotnet/dotnet dotnet restore --no-dependencies /home/REDACTED/work/OneWare/OneWare/src/VtNetCore.Avalonia/VtNetCore.Avalonia.App/VtNetCore.Avalonia.App.csproj --packages /tmp/codeql-scratch-4731918ca57aa503/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/tmp/codeql-scratch-4731918ca57aa503/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/tmp/codeql-scratch-4731918ca57aa503/dbs/csharp/working/emptyFakeDotnetRoot /p:AllowMissingPrunePackageData=true (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)