Prevent tap dance from wiping dynamic macros

[jasonkena]

Description

This pull request introduces the userspace function dynamic_macro_valid_key_user to allow the user to omit certain events from being stored in the dynamic macros. This is particularly important when DYN_* keycodes are mapped to tap-dance keys; prior to these changes, DYN_* keys (e.g. DYN_REC_START* and DYN_REC_STOP are triggered upon executing the macro (since TD(DYN) records are stored in the buffer), leading to the bug where recorded macros can only be executed once before they are wiped.

An example keymap implemented using this function is available here.

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

Checklist

• My code follows the code style of this project: C, Python
• 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).