Document not relocating Kotlin stdlib and reflect

[Goooler]

• Closes Relocated kotlin-reflect error like: Built-in class shadow.kotlin.Any is not found #1622.
• Closes Test relocating kotlin-reflect library #1695.

[Copilot]

Pull Request Overview

This PR adds documentation to discourage relocating Kotlin Standard Library and Reflect packages in the Shadow plugin configuration guide. The change addresses user questions and issues by providing clear guidance on why these specific Kotlin libraries should not be relocated.

• Adds a new documentation section explaining the risks of relocating Kotlin stdlib and reflect
• References GitHub issues #1622 and #1695 for additional context and discussion

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[shanshin]

Let's rephrase to something like this: "It is not recommended to relocate Kotlin Standard Library if you are using Kotlin Metadata or Kotlin Reflect in the project ..."

I reformulated it this way because:

• for most simple cases, the stdlib relocation does not disrupt the application
• kotlin reflect can be relocated
• In addition to Reflect, Kotlin Metadata may also be disrupted

[Goooler]

Done.

[shanshin]

Also, I think it should be called Relocating Kotlin Standard Library because this paragraph does not mention the relocation of Reflect itself.

[Goooler]

Done.

[shanshin]

Should we add links to Kotlin Metadata and Kotlin Reflect?
https://kotlinlang.org/docs/metadata-jvm.html, https://kotlinlang.org/docs/reflection.html

[Goooler]

Sure! Done.