Migrate `test-proxy` sanitizers to compile and cache regex

[scbedd]

We new up a regex every time we utilize a sanitizer. These Regex should A) be compiled and B) re-used instead of newed up within https://github.com/Azure/azure-sdk-tools/blob/e32ed540089af9d0a97eae75a2c12600b12f4708/tools/test-proxy/Azure.Sdk.Tools.TestProxy/Common/StringSanitizer.cs#L71.

[scbedd]

Completed in #13548