Activate reduced shader mode in SkiaGlRenderEngine

Test: build with https://skia-review.googlesource.com/c/skia/+/416299 and use perfetto to count
shaders compiled in cache warming step, expect 51, not 83.

Bug: b/187535297

Change-Id: Iffd827ba8fbb6f6ec4fa961f11eb920b1a26bcc2
diff --git a/libs/renderengine/skia/SkiaGLRenderEngine.cpp b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
index 2d80c46..18561da 100644
--- a/libs/renderengine/skia/SkiaGLRenderEngine.cpp
+++ b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
@@ -315,6 +315,7 @@
     GrContextOptions options;
     options.fDisableDriverCorrectnessWorkarounds = true;
     options.fDisableDistanceFieldPaths = true;
+    options.fReducedShaderVariations = true;
     options.fPersistentCache = &mSkSLCacheMonitor;
     mGrContext = GrDirectContext::MakeGL(glInterface, options);
     if (useProtectedContext(true)) {