feat: side menu "half open" support

# Feature Request

**Ionic version:**

[x] **5.x**

**Describe the Feature Request**

I would really like a Solution to have a "half open" side menu. visual example explained in this question: https://stackoverflow.com/questions/46835554/angular-material-side-bar-with-half-side-mode

**Describe Preferred Solution**

- In the best case this can be enabled for phones, tablets and desktop individually
- The "half open" state should replace the "closed" state
- The Width should be editable (via scss variables?)
- The gesture should automatically fade out labels and only keep the icons?
- The icons should still be clickable and work in that state

Start by reviewing the Ionic v5 side-menu documentation and the linked Stack Overflow example. No implementation file or test is named; define how the half-open state, responsive availability, configurable width, label fading, and icon interaction should behave, then use those requirements as the completion criteria.

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