Message parsing / validation and generation

[steven-bellock]

There are currently portions of an SPDM message that libspdm does not generate or parse. Two examples are MEASUREMENTS.MeasurementRecord and CAPABILITIES.SupportedAlgorithms. These functions are considered helper functions or tools, and would assist an Integrator in interacting with portions of an SPDM message.

This is a proposal for a new core library, call it spdm_tools_lib, that an Integrator can link against to use these parsing / generation tools.