feat: add convert_file_src function to path module

[LouisLau-art]

Summary

Adds a new public method PathResolver::convert_file_src that converts a file path to a Tauri asset URL. This function is useful when you need to reference local files in your frontend (e.g., in markdown editors where you're parsing markdown to HTML in Rust).

Implementation

• Uses dunce to canonicalize paths (normalizes paths like C:\ on Windows)
• Uses percent-encoding to URL-encode the path
• All dependencies (dunce, percent-encoding) are already in Cargo.toml

Platform-specific behavior

• Windows and Android: Returns URLs in format http://asset.localhost/<path>
• Other platforms: Returns URLs in format asset://localhost/<path>

Example usage

```rust
use tauri::Manager;
use std::path::Path;

tauri::Builder::default()
.setup(|app| {
let path = Path::new("/path/to/image.png");
let asset_url = app.path().convert_file_src(path)?;
println!("Asset URL: {}", asset_url);
Ok(())
});
```

Motivation

Previously, users had to manually call the JavaScript version of convertFileSrc() from Rust, which was hacky. This provides a native Rust way to convert file paths to Tauri asset URLs.

Closes #12022

[github-actions]

Package Changes Through fb2d3fc

There are 9 changes which include tauri with minor, @tauri-apps/cli with minor, tauri-cli with minor, tauri-utils with patch, tauri-build with patch, tauri-macos-sign with patch, tauri-bundler with minor, tauri-runtime-wry with minor, tauri-runtime with minor

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
tauri-utils	2.8.1	2.8.2
tauri-macos-sign	2.3.2	2.3.3
tauri-bundler	2.7.5	2.8.0
tauri-runtime	2.9.2	2.10.0
tauri-runtime-wry	2.9.3	2.10.0
tauri-codegen	2.5.2	2.5.3
tauri-macros	2.5.2	2.5.3
tauri-plugin	2.5.2	2.5.3
tauri-build	2.5.3	2.5.4
tauri	2.9.5	2.10.0
@tauri-apps/cli	2.9.6	2.10.0
tauri-cli	2.9.6	2.10.0

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[Legend-Master]

Hey, thanks for contributing

It seems like someone has been working on this already at #14786

[LouisLau-art]

Thanks for the heads-up! I see #14786 covers this. I'll close this PR to avoid duplication. Happy to help review or contribute there if needed.