[1.x] Migrate the test suite from Jest to Vitest

[lordrip]

Target branch: 1.x (currently v1.8.0, maintenance line).
The equivalent change for main is tracked separately — the two branches have
identical eslint.config.mjs, jest.config.ts and test layouts, so the work is
the same modulo the one difference noted under "Branch-specific notes".

Motivation

Kaoto (KaotoIO/kaoto) migrated packages/ui from Jest to Vitest in commit
769cc74 ("jest to vitest migration", 341 files changed). @kaoto/forms is still
on Jest, which leaves the two repositories on different runners, different setup
files and different mocking APIs — a constant source of friction when moving code
or contributors between them.

Vitest also removes the SWC/Babel double-transform this repo currently carries:
tests would run through the same Vite pipeline already used by yarn start and
yarn build:site.

Current state on 1.x

• Runner: Jest 29 + @swc/jest, config in jest.config.ts, setup in jest-setup.ts

• 51 test files under src/, 14 snapshot files

• 30 files reference the jest global:

  API	occurrences
  jest.fn	148
  jest.spyOn	22
  jest.clearAllMocks	7
  jest.restoreAllMocks	5
  jest.Mock (type)	5
  jest.mock	4
  jest.useFakeTimers / useRealTimers	2 / 2
  jest.requireMock	2
  jest.requireActual, jest.runAllTimers, jest.advanceTimersByTime, jest.MockedFunction	1 each

Branch-specific notes

1.x's jest-setup.ts contains a ResizeObserver mock that main does not have.
Port it to vitest-setup.ts as well — Kaoto's vitest-setup.ts implements it as a
class (ResizeObserverMock with observe/unobserve/disconnect as vi.fn()),
which avoids the arrow-function-as-constructor problem.

1.x also uses jest.requireMock in two places; main does not.

Scope

1. Config — replace jest.config.ts with vitest.config.mts modelled on
   packages/ui/vitest.config.mts in Kaoto: globals: true, environment: 'jsdom',
   include: ['**/?(*.)+(test).[tj]s?(x)'], testTimeout: 10_000, clearMocks: true,
   and server.deps.inline for @patternfly/* (replaces the current
   transformIgnorePatterns). Vite's own CSS/asset handling replaces the
   moduleNameMapper entries pointing at src/__mocks__/styleMock.ts and fileMock.ts.
2. Setup — port jest-setup.ts to vitest-setup.ts: @testing-library/jest-dom/vitest,
   vi in place of jest, and vitest-fetch-mock for the window.fetch mock. The SVG
   mocks (getScreenCTM, getBBox, getComputedTextLength, createSVGMatrix),
   matchMedia, crypto, ResizeObserver and scrollIntoView mocks carry over.
3. Test files — jest.* → vi.*; jest.Mock / jest.MockedFunction → Mock /
   MockedFunction imported from vitest; jest.requireActual → await vi.importActual(...);
   jest.requireMock → await vi.importMock(...). Note vi.mock() is hoisted with
   stricter rules than jest.mock() — factories cannot close over outer variables.
4. Published ./testing entrypoint — src/form/testing/FieldTestProvider.tsx and
   src/form/testing/FormWrapper.tsx use jest.fn() as default prop values. This is
   shipped to consumers via @kaoto/forms/testing, so it must not depend on any runner
   global. Replace with plain no-op functions (() => {}) rather than swapping in vi.fn().
5. Coverage — swap coverageProvider: 'babel' for @vitest/coverage-v8, preserving
   the current collectCoverageFrom include/exclude list.
6. Snapshots — expect churn; Vitest's serializer differs slightly from Jest's
   (the Kaoto migration touched every .snap file).
7. Cleanup — drop jest, jest-environment-jsdom, @swc/jest, babel-jest,
   @types/jest, @babel/*, babel.config.cjs, and src/__mocks__/ if unused.
8. Scripts — "test": "vitest run --config vitest.config.mts" plus a
   "test:watch" counterpart, matching Kaoto.

Acceptance criteria

• yarn test runs the full suite on Vitest with no Jest dependency left in package.json
• Coverage is still collected with the same include/exclude set
• No jest global referenced anywhere under src/, especially in src/form/testing/
• Consumers of @kaoto/forms/testing still build (KaotoFormPageObject is imported by Kaoto's packages/ui)

Reference

• Kaoto migration commit: KaotoIO/kaoto@769cc74
• Kaoto config: packages/ui/vitest.config.mts, packages/ui/vitest-setup.ts,
  packages/ui/vitest-mocks-setup.ts