Add ServiceRegistry to help migration

[a1q123456]

High Level Overview of Change

This PR adds a service registry class.

Context of Change

We're passing Application around and the Application class acts more like a service registry that gives other classes access to other services. In order to allow modularisation, we should replace Application with a service registry class so that modules depending on Application for other services can be moved easily.

This PR is part of the modularisation of the transactors. See all PRs here:
#6222
#6223
#6224
#6225
#6226
#6227
#6228

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.9%. Comparing base (7813683) to head (e14cffa).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #6222   +/-   ##
=======================================
  Coverage     79.9%   79.9%           
=======================================
  Files          839     840    +1     
  Lines        65546   65548    +2     
  Branches      7269    7266    -3     
=======================================
+ Hits         52346   52348    +2     
  Misses       13200   13200           

Files with missing lines	Coverage Δ
include/xrpl/core/ServiceRegistry.h	100.0% <100.0%> (ø)
src/xrpld/app/main/Application.h	100.0% <ø> (ø)

... and 2 files with indirect coverage changes

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[bthomee]

@vvysokikh1 how does this look to you?

[vvysokikh1]

I don't have any concrete numbers on how this will affect performance, but this change adds another layer of virtual dispatch into the picture. Considering functions from application being called multiple times anywhere in a hot path, I'd suggest we consider something like CRTP to design the registry (that should accept app as a template param).

[bthomee]

There's an unrelated file, src/xrpld/app/tx/detail/Taker.h with only whitespace changes (according to the "New GitHub Experience") or no changes (according to the legacy experience) included in this PR. The file curiously is actually empty.

I would suggest to revert the modification to the empty file in this PR, and then to delete it later as part of a modularization PR.