Support Google Play 16 KB Page Size Requirement (#13470)

- See: https://developer.android.com/guide/practices/page-sizes#update-packaging
- Also, make min API uniform at 21 (from 16 and 23 in a few places)

(cherry picked from commit dc2c83c383)

build-scripts/androidbuildlibs.sh

@@ -30,6 +30,7 @@ abi="arm64-v8a" # "armeabi-v7a arm64-v8a x86 x86_64"
 obj=
 lib=
 ndk_args=
+flexpage=true
 
 # Allow an external caller to specify locations and platform.
 while [ $# -gt 0 ]; do
@@ -42,6 +43,8 @@ while [ $# -gt 0 ]; do
         platform=${arg#APP_PLATFORM=}
     elif [ "${arg:0:8}" == "APP_ABI=" ]; then
         abi=${arg#APP_ABI=}
+    elif [ "${arg:0:32}" == "APP_SUPPORT_FLEXIBLE_PAGE_SIZES=" ]; then
+        flexpage=${arg#APP_SUPPORT_FLEXIBLE_PAGE_SIZES=}
     else
         ndk_args="$ndk_args $arg"
     fi
@@ -67,6 +70,9 @@ done
 # APP_* variables set in the environment here will not be seen by the
 # ndk-build makefile segments that use them, e.g., default-application.mk.
 # For consistency, pass all values on the command line.
+#
+# Add support for Google Play 16 KB Page size requirement:
+# https://developer.android.com/guide/practices/page-sizes#ndk-build
 ndk-build \
     NDK_PROJECT_PATH=null \
     NDK_OUT=$obj \
@@ -75,4 +81,5 @@ ndk-build \
     APP_ABI="$abi" \
     APP_PLATFORM="$platform" \
     APP_MODULES="SDL3" \
+    APP_SUPPORT_FLEXIBLE_PAGE_SIZES="$flexpage" \
     $ndk_args