Add support for sending back background and foreground command results for RUN_COMMAND intent and foreground command results for Termux:Tasker

Previously, termux only supported getting result of BACKGROUND commands back if they were started via Termux:Tasker plugin. Getting back result of foreground commands was not possible with any way.

Now with RUN_COMMAND intent or Termux:Tasker, the third party apps and users can get the foreground command results as well. Note that by "foreground results" we only mean the session transcript. The session transcript will contain both stdout and stderr combined, basically anything sent to the the pseudo terminal /dev/pts, including PS1 prefixes for interactive sessions. Getting separate stdout and stderr can currently only be done with background commands.

Moreover, with RUN_COMMAND intent, third party apps and users can get the background commands results as well. This means separate extras for stdout and stderr.

The exit code will also be returned for either case.

### RUN_COMMAND intent

The result extras are returned in the TERMUX_SERVICE.EXTRA_PLUGIN_RESULT_BUNDLE bundle via the pending intent received.

The RUN_COMMAND_SERVICE.EXTRA_PENDING_INTENT extra can be used to send the pending intent with which termux should return the result bundle. The pending intent can be received back by the app with an IntentService. Check RunCommandService for reference implementation.

For foreground commands (RUN_COMMAND_SERVICE.EXTRA_BACKGROUND is false):
- EXTRA_PLUGIN_RESULT_BUNDLE_STDOUT will contain session transcript.
- EXTRA_PLUGIN_RESULT_BUNDLE_STDERR will be null since its not used.
- EXTRA_PLUGIN_RESULT_BUNDLE_EXIT_CODE will contain exit code of session.

For background commands (RUN_COMMAND_SERVICE.EXTRA_BACKGROUND is true):
- EXTRA_PLUGIN_RESULT_BUNDLE_STDOUT will contain stdout of commands.
- EXTRA_PLUGIN_RESULT_BUNDLE_STDERR will contain stderr of commands.
- EXTRA_PLUGIN_RESULT_BUNDLE_EXIT_CODE will contain exit code of command.

The internal errors raised by termux outside the shell will be sent in the the EXTRA_PLUGIN_RESULT_BUNDLE_ERR and EXTRA_PLUGIN_RESULT_BUNDLE_ERRMSG extras. These will contain errors like if starting a termux command failed or if the user manually exited the termux sessions or android killed the termux service before the commands had finished executing. The err value will be Activity.RESULT_OK(-1) if no internal errors are raised.

The stdout and stderr will be truncated from the start to max 100KB combined and errmsg will also be truncated from end to max 25KB. This is necessary to prevent TransactionTooLargeException exceptions from being raised if stdout or stderr are too large in length. The original length of stdout and stderr will be provided in EXTRA_PLUGIN_RESULT_BUNDLE_STDOUT_ORIGINAL_LENGTH and EXTRA_PLUGIN_RESULT_BUNDLE_STDERR_ORIGINAL_LENGTH extras respectively, so that the caller can check if either of them were truncated.

### Termux:Tasker

Support for Termux:Tasker for getting back result of foreground commands will require an update to it since it currently immediately returns control to plugin host app like Tasker without waiting if a foreground command is to be executed.

app/src/main/res/values/strings.xml

@@ -96,6 +96,9 @@
     <!-- Termux Execution Commands -->
     <string name="msg_executable_absolute_path">Executable Absolute Path: \"%1$s\"</string>
     <string name="msg_working_directory_absolute_path">Working Directory Absolute Path: \"%1$s\"</string>
+    <string name="error_sending_sigkill_to_process">Sending SIGKILL to process on user request or because android is killing the service</string>
+    <string name="error_failed_to_execute_termux_session_command">"Failed to execute \"%1$s\" termux session command"</string>
+    <string name="error_failed_to_execute_termux_task_command">"Failed to execute \"%1$s\" termux task command"</string>