Migrate Tabs component from Bootstrap to Mantine.

[linuspahl]

Description

Motivation and Context

We are migrating our bootstrap based components to Mantine. This PR migrates the common Tabs component and removes the preflight Tab component.

Initially I tried using an approach where we make only changes to our Tab and Tabs component and avoid any change to their usage. See 87806fb

This approach was a bit hack (empty Tab component, extracting props from children array) and I migrated the Tabs usage to the Mantine structure.

The react-bootstrap API colocated the tab button and panel content in a single <Tab> component:

<Tabs defaultActiveKey="a" activeKey={active} onSelect={setActive} animation={false}>
  <Tab eventKey="a" title="Label A">panel content</Tab>
  <Tab eventKey="b" title="Label B">panel content</Tab>
</Tabs>

The Mantine API separates the tab buttons (Tabs.List / Tabs.Tab) from the panel content (Tabs.Panel), which mirrors the underlying HTML ARIA tabs pattern:

<Tabs defaultValue="a" value={active} onChange={setActive}>
  <Tabs.List>
    <Tabs.Tab value="a">Label A</Tabs.Tab>
    <Tabs.Tab value="b">Label B</Tabs.Tab>
  </Tabs.List>
  <Tabs.Panel value="a">panel content</Tabs.Panel>
  <Tabs.Panel value="b">panel content</Tabs.Panel>
</Tabs>

/nocl - refactoring

[linuspahl]

Imo removing the navTabsStyles here improves the styling.

[linuspahl]

For example it removes the border for the tab panel.