Introduce a level of indirection and versioning in the config files

config.h was split into build_info.h and mbedtls_config.h.

• In code, use #include <mbedtls/build_info.h>. Don't include mbedtls/config.h and don't refer to MBEDTLS_CONFIG_FILE.
• In build tools, edit mbedtls_config.h, or edit MBEDTLS_CONFIG_FILE as before.
• If you had a tool that parsed the library version from include/mbedtls/version.h, this has moved to include/mbedtls/build_info.h. From C code, both headers now define the MBEDTLS_VERSION_xxx macros.

Also, if you have a custom configuration file:

• Don't include check_config.h or config_psa.h anymore.
• Don't define MBEDTLS_CONFIG_H anymore.

A config file version symbol, MBEDTLS_CONFIG_VERSION was introduced. Defining it to a particular value will ensure that Mbed TLS interprets the config file in a way that's compatible with the config file format used by the Mbed TLS release whose MBEDTLS_VERSION_NUMBER has the same value. The only value supported by Mbed TLS 3.0.0 is 0x03000000.