Add metals-extract module for dependency extraction from build tools

[olafurpg]

Previously, users had to install Bun and run the mbt-extract.ts script to extract build data. This commit introduces a new alternative to create mbt.json, a Scala CLI using more official APIs:

• Maven Artifact Resolver API (Eclipse Aether) for Maven projects
• Gradle Tooling API for Gradle projects
• Parses maven_install.json for Bazel projects (bazel query/aspects for full support)

Implements extractors for Maven, Gradle, and Bazel projects that generate mbt.json files containing dependency information for Metals.

MavenExtractor features:

• Uses Maven Artifact Resolver API (Eclipse Aether)
• Support for parent POM inheritance
• Support for multi-module projects (recursive submodule processing)
• DependencyManagement version resolution
• Property placeholder resolution (${project.version}, etc.)
• Transitive dependency resolution
• Skips test, provided, and system scope dependencies
• Uses ~/.m2/repository (or M2_REPO env var) as local cache
• Supports custom repositories defined in pom.xml

GradleExtractor features:

• Uses Gradle Tooling API with EclipseProject model
• Support for build.gradle and build.gradle.kts
• Auto-detects and uses Gradle wrapper when available
• Recursively processes child projects in multi-project builds
• Finds sources JARs in Gradle cache structure
• Deduplicates dependencies by artifact ID

BazelExtractor features:

• Support for Bazel 7.x Bzlmod naming (~ separators)
• Support for Bazel 8.x Bzlmod naming (++ and + separators)
• Support for legacy dependency_tree format (rules_jvm_external v4)
• Support for WORKSPACE mode
• Process ALL maven_install*.json files and merge results
• Download missing JARs from Maven Central using URLs in JSON
• Fallback to .m2 cache when Bazel JARs not found

CLI options:

• --scala-version Filter by Scala version (2.12, 2.13, or 3) Excludes artifacts with non-matching Scala suffixes (_2.12, _2.13, _3)

Tested against:

• bazel-bsp: 100 deps (Bazel 7.0.2)
• rules_jvm_external/bzlmod: 66 deps (Bazel 8.3.1)
• salesforce/rules_spring: 183 deps (Bazel 7.4.1)
• linafx/digital-assets: 322 deps with --scala-version 2.13
• ValdemarGr/mezel: 23 deps with --scala-version 2.13

[olafurpg]

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