fix(QSlider): fix odd behavior on key down when set vertical mode (fix: #13132)

[madosuki]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Documentation
• Code style update
• Refactor
• Build-related changes
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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:

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Other information:
close #13132

Currently(v2.7.7) QSlider behavior when on vertical mode is odd. ref https://quasar.dev/vue-components/slider#vertical

Currently behavior is when press the down arrow key then ring move to up, when press the up arrow key oppose behavior that.

I think intuitively correct behavior is when press the down arrow key then ring move to down and when press the up arrow key is oppose behavior that.

[rstoenescu]

Thanks for contributing!
Changed it a bit and merged it.