Flattening language files, adding eslint rule to catch broken text key references

[olemartinorg]

Description

I noticed that the text key used in the helpText for 'bolignummer' in the Address component was broken:

Typescript can't help us much here, because the expected type is either just any string (for text resources defined in an app) or a valid text key as defined in en.ts/nb.ts/nn.ts. However, literal strings given as a language key should always point to text keys that are defined in app-frontend, so eslint can do that (and differentiate between a variable containing a string and a literal string) to warn us when making this mistake.

Also flattening our text files is something I've been thinking about for a long time (it may look nicer with nested objects, but it's just indirection and a format you 'need to know about'). By flattening them, we get back proper autocomplete support via the typescript types, along with simpler code to look them up.

Related Issue(s)

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Verification/QA

• Manual functionality testing
  • I have tested these changes manually
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  • No automatic tests are needed here (no functional changes/additions)
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• UU/WCAG (follow these guidelines until we have our own)
  • I have tested with a screen reader/keyboard navigation/automated wcag validator
  • No testing done/necessary (no DOM/visual changes)
  • I want someone to help me perform accessibility testing
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  • Has been added/updated
  • No functionality has been changed/added, so no documentation is needed
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[bjosttveit]

This is great, I keep forgetting to add general. when using language and getting frustrated 😅

[sonarqubecloud]

Quality Gate failed

Failed conditions
1 Security Hotspot
41.4% Coverage on New Code (required ≥ 45%)

See analysis details on SonarQube Cloud