Add TOML version catalog formatter step

[mkutz]

Resolves #2916

Adds a dedicated FormatterStep for formatting and sorting Gradle version catalog (.toml) files, with no external dependencies.

Features

• Normalize spacing around = and inside inline tables { } and arrays [ ]
• Sort entries alphabetically within each section
• Sort sections in canonical order: [versions], [libraries], [bundles], [plugins]
• Preserve comments — leading comments travel with their entry during sorting; inline comments are preserved
• Multi-line inline tables — parsed correctly and joined/split based on line length
• maxLineLength (default 120, configurable) — long inline tables are split across lines (one pair per line, 2-space indent, trailing commas)
• stripQuotedKeys (opt-in, default false) — removes unnecessary quotes from keys when the bare form is valid

Usage

Gradle:

spotless {
  toml {
    target 'gradle/libs.versions.toml'
    versionCatalog()
    // or with options:
    // versionCatalog { maxLineLength(80); stripQuotedKeys(true) }
  }
}

Maven:

<toml>
  <includes>
    <include>gradle/libs.versions.toml</include>
  </includes>
  <versionCatalog />
</toml>

Known limitations

Documented in lib/src/main/java/com/diffplug/spotless/toml/TODO.md. These are valid TOML constructs that won't appear in typical Gradle version catalogs:

• Quoted keys containing =
• Dotted/quoted table headers
• Single-quoted (literal) strings in inline tables
• Triple-quoted multiline strings

Checklist

• Class name ends in Step (VersionCatalogStep)
• Public static create method returning FormatterStep
• Test class VersionCatalogStepTest using StepHarness
• Equality test using SerializableEqualityTester
• Changelog entries in all three CHANGES.md files
• spotlessApply clean
• spotbugsMain clean