[Fix]: fix glmark2 crash

- deal with legacy GLSL syntax (attribute/varying/gl_FragColor/texture2D/etc.)
- implement glGet GL_SHADER_SOURCE_LENGTH, and make sure returns
  original shader source
- expose proper extensions (GL_ARB_depth_texture)
- support env var MOBILEGL_LOG_FILE_PATH
- unit tests to test against those changes

MobileGL/MG_Test/SanityTest.cpp

@@ -7,10 +7,66 @@
 // End of Source File Header
 
 #include <gtest/gtest.h>
+#include <algorithm>
+#include <cstdlib>
+#include <filesystem>
+#include <fstream>
+#include <string>
+
+#include <MG_Backend/DirectGLES/BackendObject_DirectGLES.h>
+#include <MG_Util/Debug/Log.h>
+
+namespace {
+    void SetEnvVar(const char* name, const char* value) {
+#if defined(_WIN32)
+        _putenv_s(name, value);
+#else
+        setenv(name, value, 1);
+#endif
+    }
+
+    void UnsetEnvVar(const char* name) {
+#if defined(_WIN32)
+        _putenv_s(name, "");
+#else
+        unsetenv(name);
+#endif
+    }
+} // namespace
 
 TEST(Sanity, BasicAssertions) {
     // Expect two strings not to be equal.
     EXPECT_STRNE("hello", "world");
     // Expect equality.
     EXPECT_EQ(7 * 6, 42);
-}
+}
+
+TEST(DirectGLESSanity, AdvertisesDepthTextureForGlmarkShadowScenes) {
+    MobileGL::MG_Backend::DirectGLES::BackendObject_DirectGLES backend;
+    const auto& extensions = backend.GetRendererInfo().RendererGLInfo.Extensions;
+
+    EXPECT_NE(std::find(extensions.begin(), extensions.end(), MobileGL::E_GL_ARB_depth_texture), extensions.end());
+}
+
+TEST(LogSanity, UsesEnvOverrideForFilePath) {
+    namespace fs = std::filesystem;
+
+    MobileGL::MG_Util::Debug::Close();
+
+    const fs::path logPath = fs::temp_directory_path() / "mobilegl-log-env-override-test.log";
+    const std::string message = "mobilegl-log-env-override-regression";
+    fs::remove(logPath);
+
+    SetEnvVar("MOBILEGL_LOG_FILE_PATH", logPath.string().c_str());
+    MobileGL::MG_Util::Debug::Log("INFO", ANDROID_LOG_INFO, "%s", message.c_str());
+    MobileGL::MG_Util::Debug::Close();
+    UnsetEnvVar("MOBILEGL_LOG_FILE_PATH");
+
+    std::ifstream logFile(logPath);
+    ASSERT_TRUE(logFile.good());
+
+    const std::string contents((std::istreambuf_iterator<char>(logFile)), std::istreambuf_iterator<char>());
+    EXPECT_NE(contents.find(message), std::string::npos);
+
+    fs::remove(logPath);
+}