Fix IDisposable contract violation

Author: mbg

csharp/autobuilder/Semmle.Autobuild.Shared/Autobuilder.cs

@@ -240,7 +240,7 @@ protected Autobuilder(IBuildActions actions, TAutobuildOptions options)
             SourceArchiveDir = RequireEnvironmentVariable(EnvVars.SourceArchiveDir(this.Options.Language));
             DiagnosticsDir = RequireEnvironmentVariable(EnvVars.DiagnosticDir(this.Options.Language));
 
-            this.diagnostics = DiagnosticsStream.ForFile(Path.Combine(DiagnosticsDir, $"autobuilder-{DateTime.UtcNow:yyyyMMddHHmm}.jsonc"));
+            this.diagnostics = new DiagnosticsStream(Path.Combine(DiagnosticsDir, $"autobuilder-{DateTime.UtcNow:yyyyMMddHHmm}.jsonc"));
         }
 
         /// <summary>

csharp/extractor/Semmle.Util/ToolStatusPage.cs

@@ -157,18 +157,10 @@ public sealed class DiagnosticsStream : IDisposable
         /// Initialises a new <see cref="DiagnosticsStream" /> for a file at <paramref name="path" />.
         /// </summary>
         /// <param name="path">The path to the file that should be created.</param>
-        /// <returns>
-        /// A <see cref="DiagnosticsStream" /> object which allows diagnostics to be
-        /// written to a file at <paramname name="path" />.
-        /// </returns>
-        public static DiagnosticsStream ForFile(string path)
+        public DiagnosticsStream(string path)
         {
-            var stream = File.CreateText(path);
-            return new DiagnosticsStream(stream);
-        }
+            this.writer = File.CreateText(path);
 
-        public DiagnosticsStream(StreamWriter streamWriter)
-        {
             var contractResolver = new DefaultContractResolver
             {
                 NamingStrategy = new CamelCaseNamingStrategy()
@@ -179,8 +171,6 @@ public DiagnosticsStream(StreamWriter streamWriter)
                 ContractResolver = contractResolver,
                 NullValueHandling = NullValueHandling.Ignore
             };
-
-            writer = streamWriter;
         }
 
         /// <summary>