Added: Export additional primary TERMUX_* scoped shell environment variables

- TERMUX__ROOTFS
- TERMUX__HOME
- TERMUX__PREFIX
- TERMUX_APP__DATA_DIR (Actual app data directory path assigned by Android for the `com.termux` app returned by `ApplicationInfo`)
- TERMUX_APP__LEGACY_DATA_DIR (Expected legacy app data directory path for the `com.termux` app, mainly accessible on primary user `0` and is a symlink/bind mount to/from `TERMUX_APP__DATA_DIR`)
- TERMUX_APP__BUILD_DATA_DIR (App data directory path used by `termux-packages` `properties.sh` while building packages and `TermuxConstants.java` while building Termux app)
- TERMUX__SE_PROCESS_CONTEXT (SeLinux process context for current process)
- TERMUX_APP__SE_FILE_CONTEXT (SeLinux file context for the `TERMUX_APP__DATA_DIR`)
- TERMUX_APP__SE_INFO (Termux app seInfo tag found in selinux policy used to set app process and app data files selinux context)

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

- termux/termux-exec-package@db738a11

See also https://github.com/termux/termux-packages/blob/96eefda/scripts/properties.sh

Author: agnostic-apollo

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

@@ -1,9 +1,13 @@
 package com.termux.shared.shell;
 
 import android.content.Context;
+import android.content.pm.ApplicationInfo;
+import android.os.Build;
 
 import androidx.annotation.NonNull;
 
+import com.termux.shared.android.SELinuxUtils;
+import com.termux.shared.data.DataUtils;
 import com.termux.shared.models.errors.Error;
 import com.termux.shared.termux.TermuxConstants;
 import com.termux.shared.file.FileUtils;
@@ -57,10 +61,42 @@ public static String[] buildEnvironment(Context currentPackageContext, boolean i
         if (TERMUX_API_VERSION_NAME != null)
             environment.add("TERMUX_API_VERSION=" + TERMUX_API_VERSION_NAME);
 
+
+
         environment.add("TERM=xterm-256color");
         environment.add("COLORTERM=truecolor");
+
+        try {
+            ApplicationInfo applicationInfo = currentPackageContext.getPackageManager().getApplicationInfo(
+                TermuxConstants.TERMUX_PACKAGE_NAME, 0);
+            if (applicationInfo != null && !applicationInfo.enabled) {
+                applicationInfo = null;
+            }
+
+            if (applicationInfo != null) {
+                environment.add("TERMUX_APP__DATA_DIR=" + applicationInfo.dataDir);
+                environment.add("TERMUX_APP__LEGACY_DATA_DIR=" + "/data/data/" + applicationInfo.packageName);
+                environment.add("TERMUX_APP__BUILD_DATA_DIR=" + TermuxConstants.TERMUX_INTERNAL_PRIVATE_APP_DATA_DIR_PATH);
+
+                environment.add("TERMUX_APP__SE_FILE_CONTEXT=" + SELinuxUtils.getFileContext(applicationInfo.dataDir));
+
+                String seInfoUser = PackageUtils.getApplicationInfoSeInfoUserForPackage(applicationInfo);
+                environment.add("TERMUX_APP__SE_INFO=" + PackageUtils.getApplicationInfoSeInfoForPackage(applicationInfo) +
+                    (DataUtils.isNullOrEmpty(seInfoUser) ? "" : seInfoUser));
+            }
+
+        } catch (final Exception e) {
+            // Ignore
+        }
+
+        environment.add("TERMUX__ROOTFS=" + TermuxConstants.TERMUX_FILES_DIR_PATH);
         environment.add("HOME=" + TermuxConstants.TERMUX_HOME_DIR_PATH);
+        environment.add("TERMUX__HOME=" + TermuxConstants.TERMUX_HOME_DIR_PATH);
         environment.add("PREFIX=" + TermuxConstants.TERMUX_PREFIX_DIR_PATH);
+        environment.add("TERMUX__PREFIX=" + TermuxConstants.TERMUX_PREFIX_DIR_PATH);
+
+        environment.add("TERMUX__SE_PROCESS_CONTEXT=" + SELinuxUtils.getContext());
+
         environment.add("BOOTCLASSPATH=" + System.getenv("BOOTCLASSPATH"));
         environment.add("ANDROID_ROOT=" + System.getenv("ANDROID_ROOT"));
         environment.add("ANDROID_DATA=" + System.getenv("ANDROID_DATA"));