fix: i18n decorator property definition

[nnaydenow]

Problem:
The i18n bundle is stored as a static property in the child class where the i18n decorator is last used. This creates an issue when trying to access the static property from a parent class if it is overridden in the child class. The result might be undefined because the bundle is only stored in the class where the decorator was last used.

This issue can be observed on the https://sap.github.io/ui5-webcomponents/nightly/components/Tree/
Note: The issue is reproducible only if the ui5-tree and ui5-tree-item components are loaded. For local testing, the defined components in the bundle should be limited to just these two.

Example:

abstract class ListItem extends ListItemBase {
	@i18n("@ui5/webcomponents")
	static i18nBundle: I18nBundle;

	get _accInfo(): AccInfo {
		return {
			ariaLabel: ListItem.i18nBundle.getText(ARIA_LABEL_LIST_ITEM_CHECKBOX) // This ListItem.i18nBundle is undefined because the bundle is only registered in TreeItemBase.
		};
	}
}

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

Solution:
The loaded bundle is now stored in a bundle storage variable. A getter is defined for each property that stores a bundle in every class where i18n decorator is used. This ensures access to the bundle storage for every class where the i18n decorator is used.

[ui5-webcomponents-bot]

🎉 This PR is included in version v2.7.0-rc.0 🎉

The release is available on v2.7.0-rc.0

Your semantic-release bot 📦🚀