2a4a3ec9ea
Reland of https://github.com/flutter/engine/pull/47432 Also includes: * https://github.com/flutter/engine/pull/47617 * https://github.com/flutter/engine/pull/47637 Fixes the performance on iOS by removing blocking on compilation of shaders. From local testing this has identical before/after numbers. Additional, ensures that we don't unecessarily specialize vertex shaders and notes this restriction in the documentation. ---- Adds support for Specialization constants to Impeller for our usage in the engine. A motivating example has been added in the impeller markdown docs. Fixes https://github.com/flutter/flutter/issues/136210 Fixes https://github.com/flutter/flutter/issues/119357