Smaller reactor handle locks (flutter/engine#56768)

This reduces the amount of work that is happening inside the read/write
mutex for tracking handles in the Reactor.
1) Now gl cleanup calls happen outside of the write lock
1) Now setting gl debug texts are out of the write lock
1) Now creating objects with CreateHandle are out of the write lock

Jonah was seeing considerable time in the rwmutex, this should alleviate
some of that.


![setlabel](https://github.com/user-attachments/assets/6ebe247b-76f4-457f-b28b-70ddcd5615a8)

issue: https://github.com/flutter/flutter/issues/159177

tests: no functional change, just performance

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above.
- [x] I added new tests to check the change I am making or feature I am
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engine/src/flutter/impeller/renderer/backend/gles/reactor_gles.cc

@@ -203,7 +203,6 @@ HandleGLES ReactorGLES::CreateHandle(HandleType type, GLuint external_handle) {
   if (new_handle.IsDead()) {
     return HandleGLES::DeadHandle();
   }
-  WriterLock handles_lock(handles_mutex_);
 
   std::optional<ReactorGLES::GLStorage> gl_handle;
   if (external_handle != GL_NONE) {
@@ -211,6 +210,8 @@ HandleGLES ReactorGLES::CreateHandle(HandleType type, GLuint external_handle) {
   } else if (CanReactOnCurrentThread()) {
     gl_handle = CreateGLHandle(GetProcTable(), type);
   }
+
+  WriterLock handles_lock(handles_mutex_);
   handles_[new_handle] = LiveHandle{gl_handle};
   return new_handle;
 }
@@ -266,41 +267,56 @@ bool ReactorGLES::ReactOnce() {
 bool ReactorGLES::ConsolidateHandles() {
   TRACE_EVENT0("impeller", __FUNCTION__);
   const auto& gl = GetProcTable();
-  WriterLock handles_lock(handles_mutex_);
-  std::vector<HandleGLES> handles_to_delete;
-  for (auto& handle : handles_) {
-    // Collect dead handles.
-    if (handle.second.pending_collection) {
-      // This could be false if the handle was created and collected without
-      // use. We still need to get rid of map entry.
-      if (handle.second.name.has_value()) {
-        CollectGLHandle(gl, handle.first.type, handle.second.name.value());
+  std::vector<std::tuple<HandleGLES, std::optional<GLStorage>>>
+      handles_to_delete;
+  std::vector<std::tuple<DebugResourceType, GLint, std::string>>
+      handles_to_name;
+  {
+    WriterLock handles_lock(handles_mutex_);
+    for (auto& handle : handles_) {
+      // Collect dead handles.
+      if (handle.second.pending_collection) {
+        handles_to_delete.push_back(
+            std::make_tuple(handle.first, handle.second.name));
+        continue;
       }
-      handles_to_delete.push_back(handle.first);
-      continue;
-    }
-    // Create live handles.
-    if (!handle.second.name.has_value()) {
-      auto gl_handle = CreateGLHandle(gl, handle.first.type);
-      if (!gl_handle) {
-        VALIDATION_LOG << "Could not create GL handle.";
-        return false;
+      // Create live handles.
+      if (!handle.second.name.has_value()) {
+        auto gl_handle = CreateGLHandle(gl, handle.first.type);
+        if (!gl_handle) {
+          VALIDATION_LOG << "Could not create GL handle.";
+          return false;
+        }
+        handle.second.name = gl_handle;
       }
-      handle.second.name = gl_handle;
-    }
-    // Set pending debug labels.
-    if (handle.second.pending_debug_label.has_value() &&
-        handle.first.type != HandleType::kFence) {
-      if (gl.SetDebugLabel(ToDebugResourceType(handle.first.type),
-                           handle.second.name.value().handle,
-                           handle.second.pending_debug_label.value())) {
+      // Set pending debug labels.
+      if (handle.second.pending_debug_label.has_value() &&
+          handle.first.type != HandleType::kFence) {
+        handles_to_name.push_back(std::make_tuple(
+            ToDebugResourceType(handle.first.type),
+            handle.second.name.value().handle,
+            std::move(handle.second.pending_debug_label.value())));
         handle.second.pending_debug_label = std::nullopt;
       }
     }
+    for (const auto& handle_to_delete : handles_to_delete) {
+      handles_.erase(std::get<0>(handle_to_delete));
+    }
   }
-  for (const auto& handle_to_delete : handles_to_delete) {
-    handles_.erase(handle_to_delete);
+
+  for (const auto& handle : handles_to_name) {
+    gl.SetDebugLabel(std::get<0>(handle), std::get<1>(handle),
+                     std::get<2>(handle));
   }
+  for (const auto& handle : handles_to_delete) {
+    const std::optional<GLStorage>& storage = std::get<1>(handle);
+    // This could be false if the handle was created and collected without
+    // use. We still need to get rid of map entry.
+    if (storage.has_value()) {
+      CollectGLHandle(gl, std::get<0>(handle).type, storage.value());
+    }
+  }
+
   return true;
 }