Feature request: Display `<name lang="...">` values from the theme in the layer selector

[troNpo]

First of all, thank you very much for the implementation made in the previous issue:
#136
The improvement works very well and the difference in user experience is noticeable. I can already confirm it in OruxMaps iOS.

Following that implementation, I would like to propose an additional enhancement related to how the layers defined in Mapsforge themes are displayed.

Description

In Mapsforge themes, the <stylemenu> block defines the layers that can be enabled or disabled in the interface. Each layer includes <name lang="..."> elements that contain the human‑readable text that should be shown to the user, with support for multiple languages.

Example:

<layer id="elv-h_routes" enabled="true">
    <name lang="es" value="[R] Rutas en BTT" />
    <name lang="en" value="[R] Mountain bike routes" />
    <cat id="h_routes" />
</layer>

Currently, the mapsforge_flutter layer selector displays the internal category identifiers (mtb_routes, c_routes, other_refs, etc.) instead of the values defined in the <name> elements of the theme.

Current behavior

• The selector shows the internal IDs of the categories.
• The names defined by the theme author are not used.
• The translations included in the theme file are not applied.

(Screenshot from OruxMaps iOS)

Ideal behavior

• Display in the interface the text defined in <name lang="..."> according to the user’s selected language.
• If the language is not available in the theme, use the default language of the <stylemenu> or the first available <name>.
• Show readable and theme‑consistent labels instead of technical identifiers.

(Screenshot from OruxMaps GP Android) This is how the native Mapsforge libraries handle it.

Technical justification

• The Mapsforge standard defines <name lang="..."> elements as the official source of text to be displayed in the UI.
• Themes such as Elevate or Voluntary rely on these names to provide a coherent and localized experience.
• Native Mapsforge libraries do use these values, so implementing this would increase compatibility and fidelity with the original themes.

Thanks in advance.