Android: Load fonts from assets

Now fonts/ directory is bundled in APK as assets. TTF_OpenFont() can
open files in Android assets, but cannot handle the "./" path prefix.

android/app/build.gradle

@@ -34,6 +34,12 @@ android {
     if (!project.hasProperty('EXCLUDE_NATIVE_LIBS')) {
         sourceSets.main {
             jniLibs.srcDir 'libs'
+            assets.srcDir '../../fonts'
+        }
+        aaptOptions {
+            // Disable asset compression for fonts.
+            // Without this, text rendering will be very slow.
+            noCompress 'ttf'
         }
         externalNativeBuild {
             cmake {