1487442 - Update highlighter instantiation methods to have clearer naming

Status: NEW

(DevTools :: Inspector, enhancement, P3)

Description

[Yulia Startsev [:yulia]]

After https://bugzilla.mozilla.org/show_bug.cgi?id=1447490, we will move to using the inspector front for managing the creation and destruction of highlighters. At the moment we do it several ways

here on the server we do it for the eyedropper
https://searchfox.org/mozilla-central/source/devtools/server/actors/inspector/inspector.js#269

and here is what we do in highlighters-overlay: https://searchfox.org/mozilla-central/source/devtools/client/inspector/shared/highlighters-overlay.js#924-933

note  we are not destroying in the second case, we are just forgetting about them. 

The "getHighlighterByType" method is always returning a new highlighter. But this doesn't make sense with the verb "get". It should be "create". The memoized function, currently called "getOrCreateHighlighterByType" should be renamed to "getHighlighterByType".