Implements customElements.getName() and fixes letter case handling.

[mash-graz]

Adding the getName() method was a rather trivial task, but it doesn't make much sense without trying to fix the much more complicated letter case resp. case-sensitivity issues regarding the custom element registry, because otherwise we would return an invalid identifier.

The custom element specification requires names, that do not contain capital ASCII letters and case-sensitive letters of some Unicode ranges. It's closer the XML conventions than traditional HTML. To emphasize this difference I also used the variable name localName instead of tagName in the relevant code sections, because element.tagName will always use capital letters, while the corresponding localName mostly uses lowercase.

Fixes: #1176

[capricorn86]

I'm looking into this. Still some more things I want to check.

[mash-graz]

I'm looking into this. Still some more things I want to check.

There is no hurry. :)

Unfortunately I'm also rather busy with other jobs. Therefor I also couldn't review your extensive node-dependency-reduction-solution util now, but I will take a look as soon as possible.