chore: migrate to nx 19

[Hotell]

NX Release announcement:

• v18 https://nx.dev/blog/2024-02-15-launch-week-recap
• v19 - Release announcement https://nx.dev/blog/nx-19-release

Other Changes:

• re-generates playwright nx-plugin executor schema based on v18 @nx/playwright changes
• normalizes nx config via nx repair
• fixes openHandles issues when running jest that started permanently failing CI https://github.com/nrwl/nx/issues/23435#issuecomment-2152900336
• adds proper component generator test for better coverage
• updates contribution guidelines to directly invoke our plugin generators

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Follows:

• https://github.com/microsoft/fluentui/pull/31746
• https://github.com/microsoft/fluentui/pull/31892