flow Implicit support for proper namespaces for svg and mathml elements

Description

Html5 doesn't require namespace declarations for svg and math elements, but as elements are created with JS in Flow, they are incorrectly handled with Flow, in case one tries to create those elements with Element API. This change adds a tiny bit of intelligence to the front end so that svg and math elements implicitly get the right namespace and other elements default to inheriting it from the parent.

Fixes #2842 to some extent. Some trivial cases work, but for proper support we should also somehow get rid of lowercasing property names.

SvgElement and usage drafted in https://github.com/viritin/flow-viritin/commit/f360f556c61ef4c66eff8f73ff6ec2a459bc326e (needs a Flow version with these changes).

Type of change

[ ] Bugfix
[x] Feature

Checklist

[ ] I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
[ ] I have added a description following the guideline.
[ ] The issue is created in the corresponding repository and I have referenced it.
[ ] I have added tests to ensure my change is effective and works as intended.
[ ] New and existing tests are passing locally with my change.
[ ] I have performed self-review and corrected misspellings.