floem localization api

localization-api.rs

```rust
use floem::prelude::*;

fn main() {
    floem::launch(app_view);
}

fn app_view() -> impl IntoView {
    // Create bundles for all supported languages
    let bundles = vec![
        L10nBundle::new("en-US", &[
            include_str!("locales/en-US.ftl"),
            include_str!("locales/common.ftl"),
        ]),
        L10nBundle::new("fr-FR", &[
            include_str!("locales/fr-FR.ftl"),
            include_str!("locales/common.ftl"),
        ]),
        L10nBundle::new("ja-JP", &[
            include_str!("locales/ja-JP.ftl"),
            include_str!("locales/common.ftl"),
        ]),
    ];

    v_stack((
        header_view(),
        content_view(),
        footer_view(),
    ))
    .style(|s| s
        .l10n_bundles(bundles)  // Inherited property - flows down to all children
        .locale("en-US")        // Inherited property - flows down to all children
        .width_full()
        .height_full()
    )
}

fn content_view() -> impl IntoView {
    let item_count = create_rw_signal(5);
    let user_name = create_rw_signal("Alice");
    let user_role = create_rw_signal("Admin");

    v_stack((
        // Simple localized text with fallback
        l10n("welcome.title")
            .style(|s| s.fallback("Welcome")),
        
        // With reactive arguments
        l10n("greeting")
            .arg("name", move || user_name.get())
            .arg("role", move || user_role.get())
            .style(|s| s.fallback("Hello, User!")),
        
        // With reactive plural count
        l10n("item-count")
            .arg("count", move || item_count.get())
            .style(|s| s.fallback("Items")),
        
        // Increment button to show reactive plural updates
        button("Add Item").on_click_stop(move |_| {
            item_count.update(|n| *n += 1);
        }),
        
        // With multiple reactive args
        l10n("notification")
            .arg("user", move || "Bob")
            .arg("action", move || "commented")
            .style(|s| s.fallback("New notification")),
    ))
    .style(|s| s.gap(10.0))
}

fn header_view() -> impl IntoView {
    l10n("app.title")
        .style(|s| s
            .font_size(24.0)
            .fallback("My Application")
        )
}

fn footer_view() -> impl IntoView {
    // Can override locale for a specific subtree
    // Uses the same inherited bundles but different locale
    l10n("footer.copyright")
        .arg("year", move || "2025")
        .style(|s| s
            .locale("ja-JP")  // Override inherited locale
            .font_size(12.0)
            .fallback("© 2025")
        )
}
```