Publish separate scip-java-proto artifact with scip.proto generated classes

[olafurpg]

Fixes #522

Previously, it was necessary to generate classes from the scip.proto source if you wanted to write Java tooling that consumes SCIP. This commit reorganizes the build so that we publish a new
com.sourcegraph:scip-java-proto artifact that only includes the generated protobuf classes from scip.proto. Note that we don't guarantee binary compatibility for public classes in this module.

Test plan

See the CI go live. I ran sbt scipProto/publishLocal and verified that the published artifact has minimal classes and minimal dependencies.

❯ cs fetch com.sourcegraph:scip-java-proto:0.8.8-2-7aafce0c-20221123-1609-SNAPSHOT

/Users/olafurpg/.ivy2/local/com.sourcegraph/scip-java-proto/0.8.8-2-7aafce0c-20221123-1609-SNAPSHOT/jars/scip-java-proto.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/protobuf/protobuf-java/3.15.6/protobuf-java-3.15.6.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/protobuf/protobuf-java-util/3.15.6/protobuf-java-util-3.15.6.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/guava/guava/30.0-android/guava-30.0-android.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/errorprone/error_prone_annotations/2.3.4/error_prone_annotations-2.3.4.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/code/gson/gson/2.8.6/gson-2.8.6.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/guava/failureaccess/1.0.1/failureaccess-1.0.1.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/guava/listenablefuture/9999.0-empty-to-avoid-conflict-with-guava/listenablefuture-9999.0-empty-to-avoid-conflict-with-guava.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/code/findbugs/jsr305/3.0.2/jsr305-3.0.2.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/checkerframework/checker-compat-qual/2.5.5/checker-compat-qual-2.5.5.jar
/Users/olafurpg/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/com/google/j2objc/j2objc-annotations/1.3/j2objc-annotations-1.3.jar

The protobuf dependencies are unavoidable.

❯ jar tf /Users/olafurpg/.ivy2/local/com.sourcegraph/scip-java-proto/0.8.8-2-7aafce0c-20221123-1609-SNAPSHOT/jars/scip-java-proto.jar

META-INF/MANIFEST.MF
com/
com/sourcegraph/
com/sourcegraph/Scip$1.class
com/sourcegraph/Scip$Descriptor$1.class
com/sourcegraph/Scip$Descriptor$Builder.class
com/sourcegraph/Scip$Descriptor$Suffix$1.class
com/sourcegraph/Scip$Descriptor$Suffix.class
com/sourcegraph/Scip$Descriptor.class
com/sourcegraph/Scip$DescriptorOrBuilder.class
com/sourcegraph/Scip$Diagnostic$1.class
com/sourcegraph/Scip$Diagnostic$2.class
com/sourcegraph/Scip$Diagnostic$Builder.class
com/sourcegraph/Scip$Diagnostic.class
com/sourcegraph/Scip$DiagnosticOrBuilder.class
com/sourcegraph/Scip$DiagnosticTag$1.class
com/sourcegraph/Scip$DiagnosticTag.class
com/sourcegraph/Scip$Document$1.class
com/sourcegraph/Scip$Document$Builder.class
com/sourcegraph/Scip$Document.class
com/sourcegraph/Scip$DocumentOrBuilder.class
com/sourcegraph/Scip$Index$1.class
com/sourcegraph/Scip$Index$Builder.class
com/sourcegraph/Scip$Index.class
com/sourcegraph/Scip$IndexOrBuilder.class
com/sourcegraph/Scip$Metadata$1.class
com/sourcegraph/Scip$Metadata$Builder.class
com/sourcegraph/Scip$Metadata.class
com/sourcegraph/Scip$MetadataOrBuilder.class
com/sourcegraph/Scip$Occurrence$1.class
com/sourcegraph/Scip$Occurrence$Builder.class
com/sourcegraph/Scip$Occurrence.class
com/sourcegraph/Scip$OccurrenceOrBuilder.class
com/sourcegraph/Scip$Package$1.class
com/sourcegraph/Scip$Package$Builder.class
com/sourcegraph/Scip$Package.class
com/sourcegraph/Scip$PackageOrBuilder.class
com/sourcegraph/Scip$ProtocolVersion$1.class
com/sourcegraph/Scip$ProtocolVersion.class
com/sourcegraph/Scip$Relationship$1.class
com/sourcegraph/Scip$Relationship$Builder.class
com/sourcegraph/Scip$Relationship.class
com/sourcegraph/Scip$RelationshipOrBuilder.class
com/sourcegraph/Scip$Severity$1.class
com/sourcegraph/Scip$Severity.class
com/sourcegraph/Scip$Symbol$1.class
com/sourcegraph/Scip$Symbol$Builder.class
com/sourcegraph/Scip$Symbol.class
com/sourcegraph/Scip$SymbolInformation$1.class
com/sourcegraph/Scip$SymbolInformation$Builder.class
com/sourcegraph/Scip$SymbolInformation.class
com/sourcegraph/Scip$SymbolInformationOrBuilder.class
com/sourcegraph/Scip$SymbolOrBuilder.class
com/sourcegraph/Scip$SymbolRole$1.class
com/sourcegraph/Scip$SymbolRole.class
com/sourcegraph/Scip$SyntaxKind$1.class
com/sourcegraph/Scip$SyntaxKind.class
com/sourcegraph/Scip$TextEncoding$1.class
com/sourcegraph/Scip$TextEncoding.class
com/sourcegraph/Scip$ToolInfo$1.class
com/sourcegraph/Scip$ToolInfo$Builder.class
com/sourcegraph/Scip$ToolInfo.class
com/sourcegraph/Scip$ToolInfoOrBuilder.class
com/sourcegraph/Scip.class
scip.proto