feat: ion-spinner css custom properties

# Feature Request

**Ionic version:**
[x] **4.x**

**Describe the Feature Request**

Add to ion-spinner more custom properties. Now only color is available in CSS Custom Properties.

**Describe Preferred Solution**
Add to CSS Custom Properties this:

width
height
stroke
stroke-width
stroke-heigth
stroke-dashoffset

**Related Code**

Locate the ion-spinner component and inspect how its existing color CSS custom property is defined and applied. Compare the requested width, height, stroke, stroke-width, stroke-heigth, and stroke-dashoffset properties with the component's current styling, then verify that each requested property affects the spinner as expected.

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