[WebEditingTester] Add support for the find and replace bar

[WebEditingTester] Add support for the find and replace bar
https://bugs.webkit.org/show_bug.cgi?id=142247

Reviewed by Enrica Casucci.

While it's not hooked up yet in WKWebView, adding support for the
find bar to WebEditingTester will help us implement that functionality.

* WebEditingTester/AppDelegate.h:
* WebEditingTester/AppDelegate.m:
(-[WebEditingAppDelegate performTextFinderAction:]):
* WebEditingTester/MainMenu.xib:
Receive performTextFinderAction: and forward it to the frontmost WebDocumentController.

* WebEditingTester/WK2WebDocumentController.m:
(-[WK2WebDocumentController awakeFromNib]):
(-[WK2WebDocumentController performTextFinderAction:]):
(-[WK2WebDocumentController findBarView]):
(-[WK2WebDocumentController setFindBarView:]):
(-[WK2WebDocumentController isFindBarVisible]):
(-[WK2WebDocumentController setFindBarVisible:]):
(-[WK2WebDocumentController findBarViewDidChangeHeight]):
(-[WK2WebDocumentController layout]):
Implement performTextFinderAction: for WebKit2, and have a NSTextFinder
pointing at the WKWebView (currently nothing will work, but the bar will
show up). Install and uninstall the bar as needed.

* WebEditingTester/WebDocument.xib:
Don't use a full-size content view. There's no need, and it makes find
bar layout harder.

* WebEditingTester/WebDocumentController.h:
* WebEditingTester/WebDocumentController.m:
(-[WebDocumentController performTextFinderAction:]):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@181007 268f45cc-cd09-0410-ab3c-d52691b4dbfc