Allow third parties to import our .hbs files and override the hooks

[vladitasev]

Currently we have several .hbs files with inline partials, which can be overridden by other components, thus providing hooks.

However, this works only for components in our own packages. Not for third parties for 2 reasons:

• We don't ship the src/ directory, so no .hbs files at all in node_modules/
• We can't import in .hbs with mode modules resolution (although a full path can work)

Ideally people could do the following:

In MyPopup.hbs

{{>include "@ui5/webcomponents/src/Popup.hbs"}}

and then override the hooks