fix: i18n bundle storage

[nnaydenow]

With the introduction of i18n storage, all loaded bundles are now stored within UI5Element (PR #10521). This storage mechanism allows child components of a UI5Element to share localization data, but the final stored bundle depends on which component loads its bundle last.

Example:

class Example extends UI5Element {
  @i18n("@ui5/webcomponents")
  static i18nBundle: I18nBundle;
}

class Example2 extends UI5Element {
  @i18n("@ui5/webcomponents-fiori")
  static i18nBundle: I18nBundle;
}

Previously, when accessing i18nBundle, the storage would always return @ui5/webcomponents-fiori, since bundles were stored under a shared key, leading to overwrites.

With this change, bundles are now stored with their bundle names. As a result:

• Example2.i18nBundle will correctly access the @ui5/webcomponents-fiori bundle.
• Example.i18nBundle will correctly access the @ui5/webcomponents bundle.

This ensures that each component retrieves the correct localization data.

Fixes: #10808