libm-v0.2.9

Fixed

• Update exponent calculations in nextafter to match musl

Changed

• Update licensing to MIT AND (MIT OR Apache-2.0), as this is derivative from
  MIT-licensed musl.
• Set edition to 2021 for all crates
• Upgrade all dependencies

Other

• Don't deny warnings in lib.rs
• Rename the musl-bitwise-tests feature to test-musl-serialized
• Rename the musl-reference-tests feature to musl-bitwise-tests
• Move musl-reference-tests to a new libm-test crate
• Add a force-soft-floats feature to prevent using any intrinsics or
  arch-specific code
• Deny warnings in CI
• Fix clippy::deprecated_cfg_attr on compiler_builtins
• Corrected English typos
• Remove unneeded extern core in tgamma
• Allow internal_features lint when building with "unstable"