abstract away the text instance dynamic array stuff and pass the correct shader when drawing quads/circles/triangles

ui.h

@@ -23,11 +23,11 @@ typedef struct TextInstance {
   float model[4][4];
 } TextInstance;
 
-typedef struct Text {
-  TextInstance *instance_data;
-  int instance_count;
-  int instance_capacity;
-} Text;
+typedef struct TextInstanceList {
+  TextInstance *data;
+  int size;
+  int capacity;
+} TextInstanceList;
 
 typedef struct Context {
   bool should_quit;
@@ -35,7 +35,7 @@ typedef struct Context {
   Size screen_size;
   Size window_size;
   ZephFont font;
-  Text texts;
+  TextInstanceList texts;
 
   Matrix4x4 projection;
 } Context;