WebCrypto types need to be cleaned up

Opening this to track this work but the fixes should live in the internal Cloudflare runtime code (either as code changes or overrides). The various operations are too generic. For example, we should export a `AesGcmParams` that has a fixed name of `AES-GCM` whereas currently we have a catch-all `SubtleCryptoEncryptAlgorithm` that is the union of all possible values. Same for things like `SubtleCryptoImportKeyAlgorithm`, `SubtleCryptoHashAlgorithm` which don't technically exist. As a nicety, we should hard-code the set of legal values for params that only have a valid set.