Added: Export ANDROID__BUILD_VERSION_SDK in shell environment variable for the Android build SDK version

This is also required for `libtermux-exec-*-ld-preload.so` `$LD_PRELOAD` library as well for `termux-exec` version `>= 2.0.0`.

- https://github.com/termux/termux-exec-package/commit/db738a11

termux-shared/src/main/java/com/termux/shared/shell/TermuxShellUtils.java

@@ -75,6 +75,8 @@ public class TermuxShellUtils {
         addToEnvIfPresent(environment, "ANDROID_RUNTIME_ROOT");
         addToEnvIfPresent(environment, "ANDROID_TZDATA_ROOT");
 
+        environment.add("ANDROID__BUILD_VERSION_SDK=" + Build.VERSION.SDK_INT);
+
         if (isFailSafe) {
             // Keep the default path so that system binaries can be used in the failsafe session.
             environment.add("PATH= " + System.getenv("PATH"));