When developing an ONNX Runtime execution provider, how to get the current `InferenceSession` instance which the execution provider registers with?

@pranavsharma is already working on this.

Since Oct 24, 2023.

### Describe the issue

When developing an ONNX Runtime execution provider, how to get the current `InferenceSession` instance which the execution provider registers with?

Seems like there is no approach to that so far?

Can we make a few changes to the class `InferenceSession` of ONNXRuntime core?

- Opiton 1
1. In the base class `IExecutionProvider`, add a new protected memeber variable `std::shared_ptr curr_sess_` and related public getter method and setter method. Then every child class of IExecutionProvider will inherit this attribute and related getter method and setter method.
2. In the method `InferenceSession::RegisterExecutionProvider()`, assign the `this` pointer to `curr_sess_` of an instance of a child class of `IExecutionProvider` using the corresponding setter method of the child class.
- Option 2
1. In a child class `MyCostumExecutionProvider`, add a new private memeber variable `std::shared_ptr curr_sess_` and related public getter method and setter method.
2. In the method `InferenceSession::RegisterExecutionProvider()` OR `InferenceSession::Initialize()`, specially handle `MyCustomExecutionProvider` to assign the `this` pointer to `MyCustomExecutionProvider::curr_sess_` using the corresponding setter method of `MyCustomExecutionProvider`. An example of specially handling a specific execution provider in `InferenceSession` class is `DmlExecutionProvider`.

### To reproduce

N/A.

### Urgency

_No response_

### Platform

All

### OS Version

All

### ONNX Runtime Installation

Other / Unknown

### ONNX Runtime Version or Commit ID

All

### ONNX Runtime API

C++

### Architecture

X64

### Execution Provider

Other / Unknown

### Execution Provider Library Version

_No response_