Mark end of version 17 and 18 C API (#20671)

Additionally, these versions are safeguarded by the `static_assert`.

Author: yihonglyu

onnxruntime/core/session/onnxruntime_c_api.cc

@@ -2723,10 +2723,14 @@ static constexpr OrtApi ort_api_1_to_18 = {
     &OrtApis::SetDeterministicCompute,
     &OrtApis::KernelContext_ParallelFor,
     &OrtApis::SessionOptionsAppendExecutionProvider_OpenVINO_V2,
+    // End of Version 17 - DO NOT MODIFY ABOVE (see above text for more information)
+
     &OrtApis::SessionOptionsAppendExecutionProvider_VitisAI,
     &OrtApis::KernelContext_GetScratchBuffer,
     &OrtApis::KernelInfoGetAllocator,
-    &OrtApis::AddExternalInitializersFromFilesInMemory};
+    &OrtApis::AddExternalInitializersFromFilesInMemory
+    // End of Version 18 - DO NOT MODIFY ABOVE (see above text for more information)
+};
 
 // OrtApiBase can never change as there is no way to know what version of OrtApiBase is returned by OrtGetApiBase.
 static_assert(sizeof(OrtApiBase) == sizeof(void*) * 2, "New methods can't be added to OrtApiBase as it is not versioned");
@@ -2755,7 +2759,8 @@ static_assert(offsetof(OrtApi, ReleaseCANNProviderOptions) / sizeof(void*) == 22
 static_assert(offsetof(OrtApi, GetSessionConfigEntry) / sizeof(void*) == 238, "Size of version 14 API cannot change");
 static_assert(offsetof(OrtApi, GetBuildInfoString) / sizeof(void*) == 254, "Size of version 15 API cannot change");
 static_assert(offsetof(OrtApi, KernelContext_GetResource) / sizeof(void*) == 265, "Size of version 16 API cannot change");
-static_assert(offsetof(OrtApi, SetUserLoggingFunction) / sizeof(void*) == 266, "Size of version 17 API cannot change");
+static_assert(offsetof(OrtApi, SessionOptionsAppendExecutionProvider_OpenVINO_V2) / sizeof(void*) == 275, "Size of version 17 API cannot change");
+static_assert(offsetof(OrtApi, AddExternalInitializersFromFilesInMemory) / sizeof(void*) == 279, "Size of version 18 API cannot change");
 
 // So that nobody forgets to finish an API version, this check will serve as a reminder:
 static_assert(std::string_view(ORT_VERSION) == "1.18.0",