Adds the `annotateElement` function to the gr-annotation library, which
applies an annotation to an element's text at the specified range as
deeply as possible.
Change-Id: I5e38a9718fc00df860e8b12a16e551ccc1b57722
The gr-diff-highlight library contained a number of generic DOM
manipulation methods that are of use elsewhere, including the variants
of `_splitNode` and `_wrapInHighlight`. This change moves these
functions into their own library called gr-annotation.js.
Change-Id: I0daf3193ef460b76e9348d6286d50a824b6a5986