Roll Flutter Engine from 78f9c6897118 to d81c4f2c759d (11 revisions) (#123664)

* 1d506dfd7 [Impeller] Allow metal shaders to compile through SPIR-V with openGL semantics. (flutter/engine#40616)

* 3287e2b36 [Impeller] support half precision uniforms and half precision samplers (flutter/engine#40590)

* 5c1c07fba Revert "Revert "Reland "Default the CanvasKit base URL to local artifacts. (#40293)" (#40470)" (#40700)" (flutter/engine#40717)

* 9e4cedc81 Forward stdout and stderr from dart2wasm when verbose. (flutter/engine#40731)

* 6941c1820 [Impeller] Allow toggling vulkan validation using a command line test flag. (flutter/engine#40728)

* 6ef595829 Roll buildroot to build CanvasKit for speed instead of code size (flutter/engine#40737)

* 5b8e02479 [Impeller] Gaussian blur: Add alpha mask specialization (flutter/engine#40707)

* 6852bea71 Roll Skia from 7311e9220faf to e3eeabb14e9c (4 revisions) (flutter/engine#40745)

* 235e42bea Add an option to malioc_diff.py to print a unified diff (flutter/engine#40732)

* 38e6d772f Roll Dart SDK from 1acd1e649fb7 to 69867ba60bb7 (2 revisions) (flutter/engine#40738)

* d81c4f2c7 [Impeller] migrate texture fill shaders to half precision. (flutter/engine#40735)

bin/internal/engine.version

-78f9c68971186f31a19d31b0212adb85938d3290
+d81c4f2c759d3ddeda8cdc68a4881d123cbbd789