src/api-impl: use skia instead of cairo

Using the C API provided by SkiaSharp's skia fork instead of using cairo
significantly improves performance. The API is also closer to the android
Canvas API, which makes the implementation more straightforward.

src/api-impl-jni/android_graphics_Paint.c

@@ -0,0 +1,27 @@
+#include <gtk/gtk.h>
+
+#include "defines.h"
+#include "util.h"
+
+#include "../sk_area/include/c/sk_paint.h"
+#include "generated_headers/android_graphics_Paint.h"
+
+JNIEXPORT jlong JNICALL Java_android_graphics_Paint_native_1constructor(JNIEnv *env, jobject this)
+{
+	return _INTPTR(sk_paint_new());
+}
+
+/* NOTE: sk_color_t seems to have the same internal representation as android uses for color, so we just pass that directly */
+JNIEXPORT void JNICALL Java_android_graphics_Paint_native_1set_1color(JNIEnv *env, jobject this, jlong skia_paint, jint color)
+{
+	sk_paint_t *paint = (sk_paint_t *)_PTR(skia_paint);
+
+	sk_paint_set_color(paint, color);
+}
+
+JNIEXPORT jint JNICALL Java_android_graphics_Paint_native_1get_1color(JNIEnv *env, jobject this, jlong skia_paint)
+{
+	sk_paint_t *paint = (sk_paint_t *)_PTR(skia_paint);
+
+	return sk_paint_get_color(paint);
+}