Add Cross Platform File Selection API

[mcmah309]

This PR adds a cross platform file selection api. Closes DioxusLabs/dioxus#3850

[Copilot]

Pull Request Overview

This PR introduces a cross-platform file selection API for Dioxus applications, enabling users to select files through a native file picker dialog.

• Adds a comprehensive file selection module with support for multiple encoding formats (base64, text, metadata-only)
• Provides both single and multiple file selection functions with configurable options
• Includes a complete example application demonstrating all file selection capabilities

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/util/src/select_file.rs	Core file selection API implementation with JavaScript bridge
packages/util/src/lib.rs	Exports the new select_file module
packages/util/Cargo.toml	Adds required dependencies for file selection functionality
examples/select_file/src/main.rs	Example application demonstrating all file selection APIs
examples/select_file/README.md	Documentation for running the example
examples/select_file/Cargo.toml	Example project configuration
README.md	Updates feature list to include file selection API

Comments suppressed due to low confidence (2)

packages/util/Cargo.toml:18

• The dependency exact_format = "0.2" appears to be added but is not used anywhere in the codebase. This dependency should either be removed or its usage should be implemented.

exact_format = "0.2"