Migrate absl::optional to std::optional in //chrome/browser/ui

- Used sed to replace the files:
  ```
  git sed absl::nullopt std::nullopt
  git sed absl::optional std::optional
  git sed 'third_party/abseil-cpp/absl/types/optional.h' '<optional>'
  ```
- Then used find and replace to fix the imports for <optional> to the
  right location
- Then git cl format

Bug: 1373619
Change-Id: I87190d65f7708bff2083e410b7209c7c60af7dcf
AX-Relnotes: n/a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5096438
Reviewed-by: David Benjamin <[email protected]>
Reviewed-by: Lei Zhang <[email protected]>
Commit-Queue: David Benjamin <[email protected]>
Auto-Submit: Mohamed Mansour <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1234337}
diff --git a/chrome/browser/ui/translate/target_language_combobox_model.h b/chrome/browser/ui/translate/target_language_combobox_model.h
index 9d09c25..5a4acf8f 100644
--- a/chrome/browser/ui/translate/target_language_combobox_model.h
+++ b/chrome/browser/ui/translate/target_language_combobox_model.h
@@ -29,7 +29,7 @@
   // Overridden from ui::ComboboxModel:
   size_t GetItemCount() const override;
   std::u16string GetItemAt(size_t index) const override;
-  absl::optional<size_t> GetDefaultIndex() const override;
+  std::optional<size_t> GetDefaultIndex() const override;
 
  private:
   const int default_index_;