Make TermuxTask and TermuxSession agnostic to termux environment

Those classes shouldn't be tied to termux environment like variables, interpreters and working directory since commands may need to be executed with a different environment like android's or with a different logic. Now both classes use the ShellEnvironmentClient interface to dynamically get the environment to be used which currently for Termux's case is implemented by TermuxShellEnvironmentClient which is just a wrapper for TermuxShellUtils since later implements static functions.

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

@@ -0,0 +1,33 @@
+package com.termux.shared.shell;
+
+import android.content.Context;
+
+import androidx.annotation.NonNull;
+
+public class TermuxShellEnvironmentClient implements ShellEnvironmentClient {
+
+    @NonNull
+    @Override
+    public String getDefaultWorkingDirectoryPath() {
+        return TermuxShellUtils.getDefaultWorkingDirectoryPath();
+    }
+
+    @NonNull
+    @Override
+    public String getDefaultBinPath() {
+        return TermuxShellUtils.getDefaultBinPath();
+    }
+
+    @NonNull
+    @Override
+    public String[] buildEnvironment(Context currentPackageContext, boolean isFailSafe, String workingDirectory) {
+        return TermuxShellUtils.buildEnvironment(currentPackageContext, isFailSafe, workingDirectory);
+    }
+
+    @NonNull
+    @Override
+    public String[] setupProcessArgs(@NonNull String fileToExecute, String[] arguments) {
+        return TermuxShellUtils.setupProcessArgs(fileToExecute, arguments);
+    }
+
+}