The key module's functionality is not used by the kernel library, but
currently kernel users are still required to initialize the key module's
`secp256k1_context_sign` global as part of the `kernel::Context` through
`ECC_Start`.
This change is mostly a refectoring that removes some code and gets rid of an
unnecessary layer of indirection after #27861
But it is not a pure refactoring since StartShutdown, AbortShutdown, and
WaitForShutdown functions used to abort on failure, and the replacement code
logs or returns errors instead.
This change helps generalize shutdown code so an interrupt can be
provided to libbitcoinkernel callers. This may also be useful to
eventually de-globalize all of the shutdown code.
Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
Co-authored-by: TheCharlatan <seb.kung@gmail.com>
* Use SECP256K1_CONTEXT_NONE when creating signing context, as
SECP256K1_CONTEXT_SIGN is deprecated and unnecessary.
* Use secp256k1_static_context where applicable.
...instead of explicitly calling init::{Set,Unset}Globals.
Cool thing about this is that in both the testing and bitcoin-chainstate
codepaths, we no longer need to explicitly unset globals. The
kernel::Context goes out of scope and the globals are unset
"automatically".
Also construct kernel::Context outside of AppInitSanityChecks()
