feat: add dom shim so importing components in SSR works

[pskelin]

Add a DOM shim so that importing web components from a server environment does not break.

This is a step towards full support of server side rendering coming with #6626

UI5Element

UI5Element now imports the shim as a first module to enable support for all components transparently.

import "@ui5/webcomponents-base/dist/ssr-dom-shim.js";
this is not a relative import on purpose, so that the conditional export in package.json can be evaluated and return the browser/node content

"exports": {
  "./dist/ssr-dom-shim.js": {
    "browser": "./dist/ssr-dom-shim-browser.js",
    "node": "./dist/ssr-dom-shim.js"
  },

Testing

There is a new script test:ssr added for main and fiori that simply imports all components and runs in node. The test will fail if the shim doesn't work or if the component is using DOM APIs in the top level of the module.

FIXES: #8106