fix($compile): use the correct namespace for transcluded svg elements

[tbosch]

This fixes the case when a directive that uses templateUrl
is used somewhere in the children
of a transcluding directive like ng-repeat.

Fixes #9344
Related to #8808

[tbosch]

@IgorMinar Could you review this?
We had multiple versions to this place in the compiler:

1. Initially we thought we could cache the namespace adapter $compileNodes.
2. Then we had the usecase where the root of the $compileNodes was a template directive with a template that is fetched slowly. So we added a check whether the content of the $compileNodes jqLite wrapper was changed to clear the cache (see When using svg directive with ngRepeat, the newly added element is not replaced with the directive template #8808 and cb73a37).
3. Now we have the usecase where a child element of the $compileNodes is a template directive with a template that is fetched slowly. Right now there is no way to detect that there is a template load pending, so we need to clone the $compileNodes in every call to the linking function if the namespace is svg.

In summary:
We cannot cache the namespace adapted $compileNodes at all.

[tbosch]

(Reviewed offline with @IgorMinar)