[v3] SaveFileDialog.SetFilename() has no effect on Linux

[samstanier]

Description

When using SaveFileDialog.SetFilename() on Linux, the filename is not pre-populated in the GTK file chooser dialog. The same code works correctly on Windows and macOS.

To Reproduce

1. Create a save file dialog with a default filename:

result, err := application.SaveFileDialog().
    SetFilename("example.txt").
    PromptForSingleSelection()
2. Run on Linux
3. Observe that the filename field in the dialog is empty


### Expected behaviour

The filename field should be pre-populated with "example.txt".


### Screenshots

_No response_

### Attempted Fixes

Extra arguments can be passed to runChooserDialog to correct this behaviour.


### System Details

```shell
Wails (v3.0.0-dev)  Wails Doctor 
                                                                                                                                                                                
# System 

┌────────────────────────────────────────────────────────────────────────────────────────┐
| Name         | Arch Linux                                                              |
| Version      | Unknown                                                                 |
| ID           | arch                                                                    |
| Branding     |                                                                         |
| Platform     | linux                                                                   |
| Architecture | amd64                                                                   |
| CPU          | Intel(R) Core(TM) i9-8950HK CPU @ 2.90GHz                               |
| GPU 1        | GP107GLM [Quadro P2000 Mobile] (NVIDIA Corporation) - Driver: nouveau   |
| GPU 2        | CoffeeLake-H GT2 [UHD Graphics 630] (Intel Corporation) - Driver: i915  |
| Memory       | 31GB                                                                    |
└────────────────────────────────────────────────────────────────────────────────────────┘

# Build Environment 

┌─────────────────────────────────────────────────────────────────────────────────────────────────────┐
| Wails CLI      | v3.0.0-dev                                                                         |
| Go Version     | go1.25.3 X:nodwarf5                                                                |
| Revision       | be60783f3a7f81366f4a60348c530dbf5d8d40b2                                           |
| Modified       | false                                                                              |
| -buildmode     | exe                                                                                |
| -compiler      | gc                                                                                 |
| CGO_CFLAGS     |                                                                                    |
| CGO_CPPFLAGS   |                                                                                    |
| CGO_CXXFLAGS   |                                                                                    |
| CGO_ENABLED    | 1                                                                                  |
| CGO_LDFLAGS    |                                                                                    |
| DefaultGODEBUG | containermaxprocs=0,decoratemappings=0,tlssha1=1,updatemaxprocs=0,x509sha256skid=0 |
| GOAMD64        | v1                                                                                 |
| GOARCH         | amd64                                                                              |
| GOEXPERIMENT   | nodwarf5                                                                           |
| GOOS           | linux                                                                              |
| vcs            | git                                                                                |
| vcs.modified   | false                                                                              |
| vcs.revision   | be60783f3a7f81366f4a60348c530dbf5d8d40b2                                           |
| vcs.time       | 2025-09-08T08:42:14Z                                                               |
└─────────────────────────────────────────────────────────────────────────────────────────────────────┘

# Dependencies 

┌──────────────────────────────────────────┐
| gcc        | 15.2.1+r301+gf24307422d1d-1 |
| gtk3       | 1:3.24.51-1                 |
| npm        | 11.6.4                      |
| pkg-config | 2.5.1-1                     |
| webkit2gtk | 2.50.4-1                    |
|                                          |
└──────── * - Optional Dependency ─────────┘

# Checking for issues 

SUCCESS  No issues found

# Diagnosis 

SUCCESS  Your system is ready for Wails development!

Need documentation? Run: wails3 docs
♥   If Wails is useful to you or your company, please consider sponsoring the project: wails3 sponsor

Additional context

In v3/pkg/application/linux_cgo.go and linux_purego.go, the runChooserDialog function never receives or uses the filename parameter. The runSaveFileDialog function has access to dialog.filename but doesn't pass it to runChooserDialog, and gtk_file_chooser_set_current_name() is never called.

[leaanthony]

This is now merged. Thanks!