Improve previewer crash recovery

[SuperJMN]

Improve stability when the previewer process crashes or cannot be started

[ForNeVeR]

Could you please explain why is this field needed? Normally the project file path is immutable, it's set once and never changes (unless the project is renamed, or something? Are you targeting such cases?).

[SuperJMN]

Makes sense; that field is gone now and we read the current projectFilePath directly from the property whenever we need it (e.g., when scheduling restarts), so there is no redundant state to keep in sync.

[SuperJMN]

Hi @ForNeVeR! I've addressed the compilation error (missing type parameter on runReadAction). The CI should pass now.

Side note: I noticed there's some pre-existing code duplication between getProjectContainingFile in AvaloniaPreviewerSessionController.kt (line 185) and the extension function in ProjectModelNodeEx.kt (line 31). Both functions do essentially the same thing. This duplication predates this PR, so I left it as-is, but it could be a good candidate for a future cleanup - the controller could simply use xamlFile.getProjectContainingFile(controllerLifetime, project) instead of having its own private copy.

[SuperJMN]

CI update: Windows and Ubuntu are now passing

The macOS failure is unrelated to code changes - it's caused by a NuGet infrastructure issue:

Unable to resolve 'Avalonia (>= 11.3.10)' for 'net8.0'.

A re-run should fix it.

[ForNeVeR]

Thanks!