feat: support decorators for custom elements metadata

[ilhan007]

The change adds support for Typescript decorators, for defining component's metadata.
Prior to this change, we used to have the static get metadata to define component's metadata. This will keep working for backward compatibility, but using decorators will be recommended from now on:

@customElement("ui5-label")
class Label extends UI5Element {
	/**
	 * Defines the labeled input by providing its ID.
	 * <br><br>
	 * <b>Note:</b> Can be used with both <code>ui5-input</code> and native input.
	 *
	 * @type {string}
	 * @defaultvalue ""
	 * @public
	 */
	@property({ type: String })
	for = "";

	/**
	 * Defines whether colon is added to the component text.
	 * <br><br>
	 * <b>Note:</b> Usually used in forms.
	 * @type {boolean}
	 * @defaultvalue false
	 * @public
	 */
	@property({ type: Boolean })
	showColon = false;
}