…3821)

Code movement and simplification, no functional changes.

Objectives:
- Allow callers specifying the needed key (or hash) size, instead of
hard-coding it in the registered PBK derivers. Conceptually, the caller
needs to specify the key size, since that is a requirement of the
(encryption) algorithm being used in the caller. Now, the code changes
here do not result in any functional changes since the key size is
always 32 bytes.
- Remove a global definition for the default PB key deriver to use.
Instead, each of the 3 use case sets the default value.

Changes:
- `crypto.DeriveKeyFromPassword` now takes a key size.
- Adds new constants for the key sizes at the callers.
- Removes the global `crypto.MasterKeySize` const.
- Removes the global `crypto.DefaultKeyDerivationAlgorithm` const.
- Adds const for the default derivation algorithms for each use case.
- Adds a const for the salt length in the `internal/user` package, to ensure
  the same salt length is used in both hash versions.
- Unexports various functions, variables and constants in the `internal/crypto`
  & `internal/user` packages.
- Renames various constants for consistency.
- Removes unused functions and symbols.
- Renames files to be consistent and better reflect the structure of the code.
- Adds a couple of tests to ensure the const values are in sync and supported.
- Fixes a couple of typos

Followups to:
- #3725
- #3770
- #3779
- #3799
- #3816

The individual commits show the code transformations to simplify the
review of the changes.