28615 Cherry-pick #28230 to fuchsia_f6 (cla: yes, platform-fuchsia)

28673 Implement a default font manager for Fuchsia. (cla: yes, platform-fuchsia)

28676 fuchsia: Convert vulkan headers to DEPS (cla: yes, platform-fuchsia)

28683 fuchsia: Use buffer_collection_x extension (cla: yes, platform-fuchsia, needs tests)

28734 [fuchsia] Fix missing function in V2 dart runner. (cla: yes, platform-fuchsia, needs tests)

28780 Revert “Replace flutter_runner::Thread with fml::Thread (#26783)” (cla: yes, platform-fuchsia, needs tests)