Add optional mod delay

[sambaum]

Description

I've copied the solution from #1037 suggested by IBNobody and integrated it into the newest version. Apparently there have been plans to create a PR, but it never got to that. So I've decided to give it a shot, because this solution really helped me and other people are also looking for a solution.
See more information here: #1037
For me the issue usually happens in the following circumstance:
Usage of nested remote access solutions, i.e. Remote-access VPN to office, then site-to-site VPN to customer, then perhaps nested RDP and/or Citrix connections.

I've been working with this solution for many weeks now and haven't encountered any issues with it. Config that I use: KEYBOARD_MOD_PACKET_DELAY 20

If the code requires changes, this PR will need the help of others, because I only have very little knowledge about C coding.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• Windows Remote Desktop Cannot Recognize Shifted Keys like KC_LPRN 100% of the time #1037
• Plans to solve the RDP issue? #18931

Checklist

• My code follows the code style of this project: C, Python (not my code, but as far as I can tell, it's following the conventions)
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[drashna]

I'm not sure that this is the correct way to handle the RDP/etc issue here.

Also, formatting:

[sambaum]

I'm not sure that this is the correct way to handle the RDP/etc issue here.

Ideally the key presses should be handled by the OS/Application correctly, but they don't, and there isn't much we can do about it, at least I didn't figure anything out. The problem does not exist with a "normal keyboard", because no one presses keys that fast.
It is kind of a workaround, which would be disabled by default. But this fix made me very happy, because my beloved custom keymap was usable again with those remote connections.

[github-actions]

Thank you for your contribution!
This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready.
For maintainers: Please label with bug, awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[github-actions]

Thank you for your contribution!
This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready.
For maintainers: Please label with bug, awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[tzarc]

Just some general paranoia.

[github-actions]

Thank you for your contribution!
This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready.
For maintainers: Please label with bug, awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[TristanCacqueray]

Thank you, that seems to work well!

Conflicts.

[dstretch]

Is this dead? I'm getting the same RDP -> RDP problem with keystrokes not registering properly...