[v3] Change KeyUsageType's Accept behavior to be by default strict, and allow toggling the feature

[lestrrat]

JWK's KeyUsageType (aka "use" field) may contain arbitrary values. Currently the behavior is not well implemented.

First, some code such as jwk.KeyUsageType.Accept reject unknown types. But key.Set() and key.UnmarshalJSON() both accept any value. This behavior should be standardized.

We should make the following changes:

• Add a global option WithStrictUsageType(bool) to enable/disable strict usage type checking. Default should be true.
• Create jwk.Settings for controlling global behavior for JWK related global options
• Create RegisterUsageType and UnregisterUsageType, which registers known usage types for strict usage type checking
• Change Accept() to change behaviors depending on the value of the above option.
• Change generated code in setNoLock() to use Accept()

Loosely/probably related to #1115