Move provider tests to onnxruntime_provider_test and enable use of plugin EPs (#25689)

### Description
<!-- Describe your changes. -->

Move provider-specific unit tests that were formerly in
`onnxruntime_test_all` to a new test program,
`onnxruntime_provider_test`. Notably, this includes the op tests which
test different provider implementations.

Enable some tests in `onnxruntime_provider_test` (those using
`ModelTester` or `OpTester`) to use a plugin EP. The plugin EP usage is
specified at runtime, so it is referred to as "dynamic". The dynamic
plugin EP configuration can be specified with environment variable
`ORT_UNIT_TEST_MAIN_DYNAMIC_PLUGIN_EP_CONFIG_JSON`.

This is an example value for
`ORT_UNIT_TEST_MAIN_DYNAMIC_PLUGIN_EP_CONFIG_JSON`. The test
infrastructure will register the plugin EP library at
`path/to/example_plugin_ep.dll`. The op tests will use a plugin EP
instance with the name `example_ep`.
```json
{
  "ep_library_registration_name": "example_ep",
  "ep_library_path": "/path/to/example_plugin_ep.dll",
  "selected_ep_name": "example_ep"
}
```

### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

Enable use of plugin EPs in some provider-specific unit tests.

Author: edgchen1

.github/workflows/linux-wasm-ci-build-and-test-workflow.yml

@@ -120,7 +120,7 @@ jobs:
           path: ${{ github.workspace }}/artifacts/wasm
 
       - name: Test (Node.js) (simd + threads)
-        # onnxruntime_test_all is currently only supported in Debug build because it requires exception, which is disabled in Release build.
+        # unit tests are currently only supported in Debug builds because they require exceptions, which are disabled in Release builds.
         if: ${{ inputs.build_config == 'Debug' }}
         run: |
           python ./tools/ci_build/build.py \
@@ -130,14 +130,14 @@ jobs:
         working-directory: ${{ github.workspace }}
 
       - name: Test (browser) (simd + threads)
-        # onnxruntime_test_all is currently only supported in Debug build because it requires exception, which is disabled in Release build.
+        # unit tests are currently only supported in Debug builds because they require exceptions, which are disabled in Release builds.
         if: ${{ inputs.build_config == 'Debug' }}
         run: |
           python ./tools/ci_build/build.py \
             ${{ env.common_build_args }} \
             --build_dir ${{ github.workspace }}/build/wasm_inferencing \
             --wasm_run_tests_in_browser \
-            --target onnxruntime_test_all \
+            --targets onnxruntime_test_all onnxruntime_provider_test \
             --update --build --test
         working-directory: ${{ github.workspace }}
 

.github/workflows/windows_webgpu.yml

@@ -127,22 +127,23 @@ jobs:
           }
           Remove-Item "${{ github.workspace }}\RelWithDebInfo" -Include "*.obj" -Recurse
 
-      - name: Run tests (onnxruntime_test_all) with verbose logging
+      - name: Run tests (onnxruntime_test_all, onnxruntime_provider_test) with verbose logging
         shell: pwsh
         run: |
           $env:ORT_UNIT_TEST_MAIN_LOG_LEVEL = "0"
-          .\onnxruntime_test_all.exe 2>.\onnxruntime_test_all_stderr.log
+          .\onnxruntime_test_all.exe 2> .\onnxruntime_test_stderr.log
+          .\onnxruntime_provider_test.exe 2>> .\onnxruntime_test_stderr.log
         working-directory: ${{ github.workspace }}\RelWithDebInfo\RelWithDebInfo
 
       - name: Check log file
         shell: cmd
         run: |
-          dir ${{ github.workspace }}\RelWithDebInfo\RelWithDebInfo\onnxruntime_test_all_stderr.log
+          dir ${{ github.workspace }}\RelWithDebInfo\RelWithDebInfo\onnxruntime_test_stderr.log
 
       - name: Validate shader keys
         uses: ./.github/actions/webgpu-validate-shader-key
         with:
-          log_file_path: ${{ github.workspace }}\RelWithDebInfo\RelWithDebInfo\onnxruntime_test_all_stderr.log
+          log_file_path: ${{ github.workspace }}\RelWithDebInfo\RelWithDebInfo\onnxruntime_test_stderr.log
 
       - name: Validate C# native delegates
         run: python tools\ValidateNativeDelegateAttributes.py

cmake/onnxruntime_test_pch.cmake

@@ -5,7 +5,10 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
   target_precompile_headers(onnxruntime_test_all PRIVATE
     "${CMAKE_CURRENT_SOURCE_DIR}/test_pch.h"
   )
-  endif()
+  target_precompile_headers(onnxruntime_provider_test PRIVATE
+    "${CMAKE_CURRENT_SOURCE_DIR}/test_pch.h"
+  )
+endif()
 
 # Exclude certain files that might conflict with PCH
 set(PCH_EXCLUDE_FILES