Tree: process events at Tree level not TreeNode level

[bill]

The onmouseenter, onmouseleave, onclick, and ondblclick events could be more efficiently processed by Tree, instead of setting up handlers for each TreeNode.

[bill]

In [28027]:

Use event delegation for Tree, fixes #14896 !strict.

[bill]

In [28310]:

Use the same on.selector() method for keyboard events as click events... it's more resilient for Trees with custom TreeNodes that have nested widgets, in which case the getEnclosingWidget() call might return one of the nested widgets rather than the TreeNode.

This also switches to pure use of dojo/on, which means that the keypress event is no longer normalized to mozilla behavior, so had to handle those browser differences myself.

Fixes #15153, refs #14896 !strict.

[Bill Keese <bill@…>]

In 50ab5342e090e9a6c03054e01ad2fc01ac0e6c1b/dijit:

Error: Processor CommitTicketReference failed

Unsupported version control system "git": Can't find an appropriate component, maybe the corresponding plugin was not enabled? 

[Bill Keese <bill@…>]

In 709054a4a415314ad102858e3e9d14e11a103f38/dijit:

Error: Processor CommitTicketReference failed

Unsupported version control system "git": Can't find an appropriate component, maybe the corresponding plugin was not enabled? 

[Bill Keese <bill@…>]

In 0f212ec839511767f18d6ead9f70c81ee8448cff/dijit:

Error: Processor CommitTicketReference failed

Unsupported version control system "git": Can't find an appropriate component, maybe the corresponding plugin was not enabled? 

[Bill Keese <bill@…>]

In 2b8acb647169c38dbe2c3d6e3f569c0847d4ea29/dijit:

Error: Processor CommitTicketReference failed

Unsupported version control system "git": Can't find an appropriate component, maybe the corresponding plugin was not enabled?