Regex perf test (#26827)

* Regex perf test

* caps

Author: danmoseley

src/System.Text.RegularExpressions/tests/Performance/Configurations.props

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <BuildConfigurations>
+      netcoreapp;
+    </BuildConfigurations>
+  </PropertyGroup>
+</Project>