Kotlin recipe DSL: preserve dot-on-its-own-line layout across chain collapse

[jkschneider]

Summary

Real-world Kotlin chains are formatted with each .member(...) on its own indented line:

xs
    .filter { p }
    .firstOrNull()

The K2 plugin's chain-collapse rewrite synthesizes a single fused call (xs.firstOrNull(p)) by applying a KotlinTemplate at the matched outer's coordinates. The result's outer-call select.after defaults to "" — the whitespace that used to sit between the inner's text end and the outer's . is lost — and the synthesized .firstOrNull(p) ends up jammed onto the previous line. Surfaced by Performance / BestPractices chain-collapse recipes in moderneinc/recipes-kotlin running against real corpora.

preserveSelectAfter copies the matched outer call's select.after onto the template-substituted result so the new outer sits on its own dot-prefixed line, matching where the matched outer originally was.

Wired into every method-invocation rewrite path so chain-shape and bare-shape rewrites both preserve the author's line layout:

• methodInvocationRewrite (bare Kotlin)
• methodInvocationRewriteJava (Java template)
• methodInvocationRewriteKotlinNotNull (K.Unary unwrap)
• chainMethodInvocationRewrite (two-segment chain)

No-op when the matched outer has no select.after whitespace (already single-line) or when the result has no select (template produced a non-method shape).

Test plan

Four new tests in RecipePluginRewriteTest:

• chain collapse preserves dot-on-its-own-line layout — positive case for the chain path (filter(p).firstOrNull() collapse with multi-line layout in the source)
• chain collapse — single-line input stays single-line (no false-positive newline) — negative case proving the empty-whitespace guard doesn't insert newlines into single-line chains
• chain collapse — alternate shape (map then filterNotNull) also preserves layout — second chain-shape variant proving the fix isn't specific to filter/firstOrNull (this is the shape that surfaced the bug)
• bare single-call rewrite preserves dot-on-its-own-line layout — exercises the non-chain methodInvocationRewrite path so we don't regress one branch while fixing another

./gradlew :rewrite-kotlin:test green.