refactor: create shared ew canvas header.

[kozmaadrian]

Description

Extracts the ew canvas header into a shared component in blocks/shared/, so the base header can back other "canvas" too, e.g. SC Editor.

• New ew-canvas-header-base: renders the bar with a built-in toggle-before button and three slots.
• ew-canvas-header (canvas): same as before, but now composes the base canvas. The undo/redo, the view toggle, and the after toggle go in via slots
• Reusable: the base can back other workspaces too, e.g. when integrating the SC Editor.
• No behavior change.

Before the change:

After the change:

Test:

• Url https://ew-shared-canvas-header--da-live--adobe.aem.live/canvas#/exp-workspace/frescopa/coffee

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

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Commits

• fee1fe8 ✅ (latest)
• e107aef ✅

[anfibiacreativa]

LGTM but the tests are failing