Initial stubs for an LSIF generator that runs as part of the normal compilation pass.

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -4773,6 +4773,8 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
 -modulename:<string>          Specify the name of the source module
 -generatedfilesout:<dir>      Place files generated during compilation in the
                               specified directory.
+-generatedartifactsout:<dir>      Place artifacts generated during compilation in the
+                              specified directory.
 </value>
     <comment>Visual C# Compiler Options</comment>
   </data>

src/Compilers/CSharp/Portable/CommandLine/CSharpCommandLineParser.cs

@@ -78,6 +78,7 @@ internal sealed override CommandLineArguments CommonParse(IEnumerable<string> ar
             string? outputRefFilePath = null;
             bool refOnly = false;
             string? generatedFilesOutputDirectory = null;
+            string? generatedArtifactsOutputDirectory = null;
             string? documentationPath = null;
             ErrorLogOptions? errorLogOptions = null;
             bool parseDocumentationComments = false; //Don't just null check documentationFileName because we want to do this even if the file name is invalid.
@@ -626,6 +627,17 @@ internal sealed override CommandLineArguments CommonParse(IEnumerable<string> ar
                             }
                             continue;
 
+                        case "generatedartifactsout":
+                            if (string.IsNullOrWhiteSpace(value))
+                            {
+                                AddDiagnostic(diagnostics, ErrorCode.ERR_SwitchNeedsString, MessageID.IDS_Text.Localize(), arg);
+                            }
+                            else
+                            {
+                                generatedArtifactsOutputDirectory = ParseGenericPathToFile(value, diagnostics, baseDirectory);
+                            }
+                            continue;
+
                         case "doc":
                             parseDocumentationComments = true;
                             if (RoslynString.IsNullOrEmpty(value))
@@ -1503,6 +1515,7 @@ internal sealed override CommandLineArguments CommonParse(IEnumerable<string> ar
                 OutputDirectory = outputDirectory!, // error produced when null
                 DocumentationPath = documentationPath,
                 GeneratedFilesOutputDirectory = generatedFilesOutputDirectory,
+                GeneratedArtifactsOutputDirectory = generatedArtifactsOutputDirectory,
                 ErrorLogOptions = errorLogOptions,
                 AppConfigPath = appConfigPath,
                 SourceFiles = sourceFiles.AsImmutable(),