feat(core): move MatchMedia to internal scope

[CaerusKaru]

BREAKING CHANGE:

• MatchMedia is no longer exported as a public utility. Please use MediaObserver instead.
• ServerMatchMedia is no longer exported at all

[willyboy]

@CaerusKaru We were using mockMatchMedia to activate different breakpoints in tests. What's the preferred approach now? I could open a docs PR with a bit of direction.

[MaT1g3R]

Hello, is there any updates on this? We are using MockMatchMedia too and we would like to know what is the preferred approach now as well, thanks.

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