[TensorRT] Support Multiple EP Context

[jingyanwangms]

Description

• Use CreateEpContextModel from graph_partitioner.cc to save model with context ep. Now multi ep context in a model is supported
• Updated merging ep context related options from session option and tensorrt option
• Updated and adding unit test

Supported scenarios:

• Save/run static single ep context node using engine cache
• Save/run static single ep context node with embedded ep context info
• Save/run static multiple ep context node using engine cache
• Save/run static multiple ep context node with embedded ep context info
• Save/run dynamic multiple ep context node using engine cache
• Save/run dynamic multiple ep context node with embedded ep context info

Unsupported scenarios:

• Subsequent runs with dynamic ep context node where dynamic input dimension changed
  Supporting this will require a call up from execution provider to CreateEpContextModel in graph_partitioner.cc during run time. It will require significant changes in the existing infrastructure.

Motivation and Context