Use body encoder instead of just blob builder for IL stream. (#23)

This removes the need for manually aligning the instructions in the IL stream, the encoder takes care of this when necessary.

Author: vitek-karas

src/coreclr/tools/ILTrim/ILTrim/DependencyAnalysis/MethodBodyNode.cs

@@ -96,8 +96,6 @@ public int Write(ModuleWritingContext writeContext)
             if (rva == 0)
                 return -1;
 
-            writeContext.ILStream.Align(4);
-
             MethodBodyBlock bodyBlock = _module.PEReader.GetMethodBody(rva);
 
             // TODO: need to rewrite token references in the exception regions
@@ -174,8 +172,7 @@ public int Write(ModuleWritingContext writeContext)
                 }
             }
 
-            MethodBodyStreamEncoder bodyStreamEncoder = new MethodBodyStreamEncoder(writeContext.ILStream);
-            MethodBodyStreamEncoder.MethodBody bodyEncoder = bodyStreamEncoder.AddMethodBody(
+            MethodBodyStreamEncoder.MethodBody bodyEncoder = writeContext.MethodBodyEncoder.AddMethodBody(
                 outputBodyBuilder.Count,
                 bodyBlock.MaxStack,
                 exceptionRegionCount: 0,

src/coreclr/tools/ILTrim/ILTrim/ModuleWriter.cs

@@ -64,7 +64,7 @@ public void Save(Stream outputStream)
             var peBuilder = new ManagedPEBuilder(
                 headerBuilder,
                 mdRootBuilder,
-                context.ILStream,
+                context.MethodBodyEncoder.Builder,
                 entryPoint: (MethodDefinitionHandle)tokenMap.MapToken(sourceEntryPoint));
 
             var o = new BlobBuilder();

src/coreclr/tools/ILTrim/ILTrim/ModuleWritingContext.cs

@@ -17,7 +17,7 @@ public sealed class ModuleWritingContext
 
         public MetadataBuilder MetadataBuilder { get; } = new MetadataBuilder();
 
-        public BlobBuilder ILStream { get; } = new BlobBuilder();
+        public MethodBodyStreamEncoder MethodBodyEncoder { get; } = new MethodBodyStreamEncoder(new BlobBuilder());
 
         public TokenMap TokenMap { get; }