In cases where we just want a random value for a primitive arithmetic
type, we can wrap this in a template to allow convenient direct
assignment instead of keeping declaration and initialization separate
(making it more difficult to use values uninitialized). This also allows
the use of Common::Random with functions such as std::generate, making
it more flexible in how random values can be generated.
This makes it easier to generate random numbers or fill a buffer with
random data in a cryptographically secure way.
This also replaces existing usages of RNG functions in the codebase:
* <random> is pretty hard to use correctly, and std::random_device does
not give enough guarantees about its results (it's
implementation-defined, non cryptographically secure and could be
deterministic on some platforms).
Doing things correctly is error prone and verbose.
* rand() is terrible and should not be used especially in crypto code.
