Unify caching story across the docs

[delbaoliveira]

This PRs unifies the caching story across the docs, making Cache Components the happy path, while still providing guidance to users in the old model. However, instead of explaining the old model and its caching layers, we've created a new guide focusing on what APIs to use and when.

This follow-up PR aligns terminology across the docs: #90589

IA updates

Getting Started section:

• Improves Getting Started progression:
  • Before: CC → Fetching Data → Updating Data → Caching and Revalidating (old and new model mixed)
  • After: Fetching Data (Dynamic) → Mutating Data (Dynamic) → Caching with CC (Prerendering) → Revalidating with CC.
• New: caching.mdx (CC-first)
  • Structure:
    • Enabling Cache Components
    • Data vs UI-level caching
    • Working with request time APIs
    • Passing request values to cached functions
    • Working with non-deterministic operations
    • Working with synchronous operations
    • How rendering works (PPR and static shell story)
• New: revalidating.mdx (CC-first)
  • Explains how to use cacheLife and cacheTag

Guides Section:

• New: caching-and-revalidating.mdx (Previous Model)
  • For users who are not using CC, includes fetch options and route segment config
  • Moves route segment config options that don't apply to CC from API reference to this guide (for easy archiving in the future).
• New: migrating-to-cache-components.mdx (WIP)
• Del: caching.mdx 😌

Terminology

We should remove caching layers from the docs. Users only needed to be exposed to them when they were configured independently, but the new CC APIs work across layers.

To make it easier to review this PR, I'm consolidating terminology and fixing broken links in a new PR: #90589

[github-actions]

All broken links are now fixed, thank you!

[icyJoseph]

LFG