Fix delegated constructor multiline formatting

[istvan-florio]

Fixes #1762.

Summary

• Preserve the existing one-line delegated constructor formatting for simple this(...) / super(...) calls.
• Expand delegated constructor calls to one argument per line when any delegated constructor argument explicitly emits multiline code.
• Cover this, super, constructor body formatting, newline string literals, and long single-line arguments with exact output tests.

Note: the multiline predicate intentionally targets explicit emitted newlines in CodeBlock formatting. String literal contents emitted via %S / %P are left on the existing path so raw/string-literal newlines do not force expanded delegated-call formatting.

Test plan

• ./gradlew :kotlinpoet:jvmTest --tests com.squareup.kotlinpoet.FunSpecTest

• ./gradlew :kotlinpoet:apiCheck

• git diff --check

• ./gradlew clean build

• docs/changelog.md has been updated if applicable.

  • Changes not visible to library consumers, such as build script, documentation, or test code updates, don't need to
    be added to the changelog.

• CLA signed.

[JakeWharton]

This wouldn't handle positional format arguments.

[JakeWharton]

Unless we normalize those on the way in. I honestly can't remember...