fix(platform-server): don't clobber parse5 properties when setting

[vikerman]

element properties.

Fixes #17050.

We now store all element properties in a separate 'properties' bag.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• [] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Setting properties like "name" on an element in platform-server will cause the rendered HTML string to have invalid tag names for the element.

Issue Number: 17050

What is the new behavior?

Setting any property on the element wouldn't cause serialization to string to break.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[mary-poppins]

You can preview 3cf275d at https://pr18237-3cf275d.ngbuilds.io/.

[alxhub]

LGTM. We should have a discussion on whether or not to consider this breaking.

[vikerman]

The plan is to merge to master and ask our Universal customers whether it would be breaking for them if we moved this to the stable branch.

[mary-poppins]

You can preview df7258f at https://pr18237-df7258f.ngbuilds.io/.

[mary-poppins]

You can preview f5b6d61 at https://pr18237-f5b6d61.ngbuilds.io/.

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