[Impeller] Fix text jitter on Vulkan.

impeller/entity/shaders/glyph_atlas.frag

@@ -11,7 +11,7 @@ uniform FragInfo {
 }
 frag_info;
 
-in vec2 v_uv;
+in highp vec2 v_uv;
 
 out f16vec4 frag_color;
 

impeller/entity/shaders/glyph_atlas.vert

@@ -3,23 +3,24 @@
 // found in the LICENSE file.
 
 #include <impeller/transform.glsl>
-#include <impeller/types.glsl>
+
+precision highp float;
 
 uniform FrameInfo {
-  mat4 mvp;
-  mat4 entity_transform;
-  vec2 atlas_size;
-  vec2 offset;
+  highp mat4 mvp;
+  highp mat4 entity_transform;
+  highp vec2 atlas_size;
+  highp vec2 offset;
   float is_translation_scale;
 }
 frame_info;
 
 // XYWH.
-in vec4 atlas_glyph_bounds;
+in highp vec4 atlas_glyph_bounds;
 // XYWH
-in vec4 glyph_bounds;
+in highp vec4 glyph_bounds;
 
-in vec2 unit_position;
+in highp vec2 unit_position;
 in highp vec2 glyph_position;
 
 out highp vec2 v_uv;

impeller/entity/shaders/glyph_atlas_color.frag

@@ -11,7 +11,7 @@ uniform FragInfo {
 }
 frag_info;
 
-in vec2 v_uv;
+in highp vec2 v_uv;
 
 out f16vec4 frag_color;