Resourceadm: fixes after update of designsystem package

[mgunnerud]

Description

• use asChild instead of as={\<comp>}
• remove visibility fix for radio button group now that hideLegend prop works as expected
• remove styling targeting all h1, h2, p elements
• use \<StudioButton> instead of \<Button>

Related Issue(s)

• this PR

Verification

• [x] Your code builds clean without any errors or warnings
• [x] Manual testing done (required)
• [x] Relevant automated test added (if you find this hard, leave it and we'll help out)

Documentation

• [ ] User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.70%. Comparing base (a9b05eb) to head (ec9dcd3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #13064 +/- ## ======================================= Coverage 91.70% 91.70% ======================================= Files 1414 1414 Lines 19935 19935 Branches 2399 2399 ======================================= Hits 18281 18281 Misses 1397 1397 Partials 257 257 ```

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