Introduce LogFlags as a independent subset of DynFlags used for logging.
As a consequence in many places we don't have to pass both Logger and
DynFlags anymore.

The main reason for this refactoring is that I want to refactor the
systools interfaces: for now many systools functions use DynFlags both
to use the Logger and to fetch their parameters (e.g. ldInputs for the
linker). I'm interested in refactoring the way they fetch their
parameters (i.e. use dedicated XxxOpts data types instead of DynFlags)
for #19877. But if I did this refactoring before refactoring the Logger,
we would have duplicate parameters (e.g. ldInputs from DynFlags and
linkerInputs from LinkerOpts). Hence this patch first.

Some flags don't really belong to LogFlags because they are subsystem
specific (e.g. most DumpFlags). For example -ddump-asm should better be
passed in NCGConfig somehow. This patch doesn't fix this tight coupling:
the dump flags are part of the UI but they are passed all the way down
for example to infer the file name for the dumps.

Because LogFlags are a subset of the DynFlags, we must update the former
when the latter changes (not so often). As a consequence we now use
accessors to read/write DynFlags in HscEnv instead of using `hsc_dflags`
directly.

In the process I've also made some subsystems less dependent on DynFlags:

- CmmToAsm: by passing some missing flags via NCGConfig (see new fields
  in GHC.CmmToAsm.Config)
- Core.Opt.*:
    - by passing -dinline-check value into UnfoldingOpts
    - by fixing some Core passes interfaces (e.g. CallArity, FloatIn)
      that took DynFlags argument for no good reason.
    - as a side-effect GHC.Core.Opt.Pipeline.doCorePass is much less
      convoluted.