feat(QCircularProgress): line-cap support

[bazuka5801]

PR for #14425
Tested on /ui yarn dev and added one example.

What kind of change does this PR introduce?

• Bugfix
• Feature
• Documentation
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the dev branch (or v[X] branch)
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)
• It's been tested on a Cordova (iOS, Android) app
• It's been tested on an Electron app
• Any necessary documentation has been added or updated in the docs or explained in the PR's description.

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to start a new feature discussion first and wait for approval before working on it)

Other information:
Add stroke-linecap to Circular Progress
stroke-linecap="round"

quasar/ui/src/components/circular-progress/QCircularProgress.js

Lines 69 to 82 in baf2f99

	function getCircle ({ thickness, offset, color, cls }) {
	return h('circle', {
	class: 'q-circular-progress__' + cls + (color !== void 0 ? ` text-${ color }` : ''),
	style: circleStyle.value,
	fill: 'transparent',
	stroke: 'currentColor',
	'stroke-width': thickness,
	'stroke-dasharray': strokeDashArray,
	'stroke-dashoffset': offset,
	cx: viewBox.value,
	cy: viewBox.value,
	r: radius
	})
	}

Example:

[rstoenescu]

Thanks for contributing!