Fix vulkan subtest for diffCtx and platform/device info (#2046)

Fixes:
1. Multi import diff ctx subtest which acquires/releases external memory
via queue not associated with the context in which memory was imported.
2. Platform/Device info subtests to handle different platforms and
availability of the query.

test_common/harness/testHarness.cpp

@@ -1294,6 +1294,43 @@ cl_platform_id getPlatformFromDevice(cl_device_id deviceID)
     return platform;
 }
 
+/**
+ * Helper to return a string containing platform information
+ * for the specified platform info parameter.
+ */
+std::string get_platform_info_string(cl_platform_id platform,
+                                     cl_platform_info param_name)
+{
+    size_t size = 0;
+    int err;
+
+    if ((err = clGetPlatformInfo(platform, param_name, 0, NULL, &size))
+            != CL_SUCCESS
+        || size == 0)
+    {
+        throw std::runtime_error("clGetPlatformInfo failed\n");
+    }
+
+    std::vector<char> info(size);
+
+    if ((err = clGetPlatformInfo(platform, param_name, size, info.data(), NULL))
+        != CL_SUCCESS)
+    {
+        throw std::runtime_error("clGetPlatformInfo failed\n");
+    }
+
+    /* The returned string does not include the null terminator. */
+    return std::string(info.data(), size - 1);
+}
+
+bool is_platform_extension_available(cl_platform_id platform,
+                                     const char *extensionName)
+{
+    std::string extString =
+        get_platform_info_string(platform, CL_PLATFORM_EXTENSIONS);
+    return extString.find(extensionName) != std::string::npos;
+}
+
 void PrintArch(void)
 {
     vlog("sizeof( void*) = %zu\n", sizeof(void *));