[Impeller] reland: directly encode blit commands for Metal. (#52819)

Fixes bad interaction with render pass clear patch, which potentially created an active blit and render pass encoder at the same time. Make sure that we start/finish the render pass before we start the blit pass.

Author: Jonah Williams

ci/licenses_golden/licenses_flutter

@@ -42656,8 +42656,6 @@ ORIGIN: ../../../flutter/impeller/renderer/backend/gles/texture_gles.cc + ../../
 ORIGIN: ../../../flutter/impeller/renderer/backend/gles/texture_gles.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/metal/allocator_mtl.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/metal/allocator_mtl.mm + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/impeller/renderer/backend/metal/blit_command_mtl.h + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/impeller/renderer/backend/metal/blit_command_mtl.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/metal/blit_pass_mtl.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/metal/blit_pass_mtl.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/metal/command_buffer_mtl.h + ../../../flutter/LICENSE
@@ -45531,8 +45529,6 @@ FILE: ../../../flutter/impeller/renderer/backend/gles/texture_gles.cc
 FILE: ../../../flutter/impeller/renderer/backend/gles/texture_gles.h
 FILE: ../../../flutter/impeller/renderer/backend/metal/allocator_mtl.h
 FILE: ../../../flutter/impeller/renderer/backend/metal/allocator_mtl.mm
-FILE: ../../../flutter/impeller/renderer/backend/metal/blit_command_mtl.h
-FILE: ../../../flutter/impeller/renderer/backend/metal/blit_command_mtl.mm
 FILE: ../../../flutter/impeller/renderer/backend/metal/blit_pass_mtl.h
 FILE: ../../../flutter/impeller/renderer/backend/metal/blit_pass_mtl.mm
 FILE: ../../../flutter/impeller/renderer/backend/metal/command_buffer_mtl.h

impeller/renderer/backend/metal/BUILD.gn

@@ -8,8 +8,6 @@ impeller_component("metal") {
   sources = [
     "allocator_mtl.h",
     "allocator_mtl.mm",
-    "blit_command_mtl.h",
-    "blit_command_mtl.mm",
     "blit_pass_mtl.h",
     "blit_pass_mtl.mm",
     "command_buffer_mtl.h",

impeller/renderer/backend/metal/blit_command_mtl.h

@@ -7,7 +7,6 @@
 
 #include <Metal/Metal.h>
 
-#include "impeller/renderer/backend/metal/blit_command_mtl.h"
 #include "impeller/renderer/blit_pass.h"
 
 namespace impeller {
@@ -20,10 +19,14 @@ class BlitPassMTL final : public BlitPass {
  private:
   friend class CommandBufferMTL;
 
-  std::vector<std::unique_ptr<BlitEncodeMTL>> commands_;
+  id<MTLBlitCommandEncoder> encoder_ = nil;
   id<MTLCommandBuffer> buffer_ = nil;
-  std::string label_;
   bool is_valid_ = false;
+  bool is_metal_trace_active_ = false;
+  // Many parts of the codebase will start writing to a render pass but
+  // never submit them. This boolean is used to track if a submit happened
+  // so that in the dtor we can always ensure the render pass is finished.
+  mutable bool did_finish_encoding_ = false;
 
   explicit BlitPassMTL(id<MTLCommandBuffer> buffer);
 
@@ -37,8 +40,6 @@ class BlitPassMTL final : public BlitPass {
   bool EncodeCommands(
       const std::shared_ptr<Allocator>& transients_allocator) const override;
 
-  bool EncodeCommands(id<MTLBlitCommandEncoder> pass) const;
-
   // |BlitPass|
   bool OnCopyTextureToTextureCommand(std::shared_ptr<Texture> source,
                                      std::shared_ptr<Texture> destination,