Migrate OSS-Fuzz back to development

[gilles-peskine-arm]

During the preparation of Mbed TLS 4.0, we pointed OSS-Fuzz to mbedtls-3.6, due to the likely instability of the development branch. The goal of this issue is to migrate OSS-Fuzz back to what will become Mbed TLS 4.0, or as applicable TF-PSA-Crypto 1.0.

We should do this as soon as APIs and build scripts have stabilized enough. In any case, This must be completed several weeks before the 4.0 release so that we have run at least one fuzz cycle with the new code.

Prerequisites: design a way to keep fuzzing bignum and ECC and implement that design.