Shortcut editor: Centralize button creation
Shortcut editor: Centralize button creation

The shortcut editor has several icon buttons that are identical in
structure (edit, delete, confirm, and cancel) but are created
separately. This CL adds a _createIconButton method to ShortcutListItem
to reduce code duplication and make it simpler to add future buttons
(e.g. a revert to defaults button).

Button examples (no visual change): https://i.imgur.com/iAFOGr3.png

Bug: 174309
Change-Id: Iae85df56d7df8785f839e4306d36dfddb2205aae
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2477337
Reviewed-by: Brian Cui <eebe54f29fdfbfde69930c5ed5d840454db62ce7@microsoft.com>
Commit-Queue: Jack Lynch <d6fb7cfbb8c8618e756350219cb7952a0ad656b7@microsoft.com>

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