feat(locale): add Norwegian Nynorsk (nn) locale

[arvindfroi]

Adds a Norwegian Nynorsk (nn) locale. Vuetify already ships Norwegian Bokmål (no); this adds the other official written standard of Norwegian.

• New packages/vuetify/src/locale/nn.ts, mirroring no.ts exactly (same key set), with all strings in Nynorsk.
• Registered nn in packages/vuetify/src/locale/index.ts (between nl and no).

Disclosure: prepared with AI assistance and reviewed by me as a native Norwegian speaker. Happy to adjust any wording.

[J-Sek]

Could you verify potential improvements:

- minLength: 'Du må skrive inn minimum {0} teikn',
+ minLength: 'Du må skrive inn minst {0} teikn',

- itemsSelected: '{0} vald',
+ itemsSelected: '{0} valde',

- lightnessInput: 'Lysheit',
+ lightnessInput: 'Lysstyrke',

- prependAction: '{0} førestilt handling',
+ prependAction: '{0} foranstilt handling',

[J-Sek]

GitHub is having partial outage and I cannot make supplemental change on your branch.
I wish to include a small change in internationalization.md:

- - **no** - Norwegian (Norsk)
+ - **nn** - Norwegian (Norsk nynorsk)
+ - **no** - Norwegian (Norsk bokmål)

[J-Sek]

just a few pieces to refine and we should be ready to merge it