[Enhancement] Extract validate and build message property methods out of sendMessageActivity into a common util class

### Before Creating the Enhancement Request

- [x] I have confirmed that this should be classified as an enhancement rather than a bug/feature.

### Summary

Extract validate and build message property methods out of sendMessageActivity into a common util class so that it can be used by other modules.

### Motivation

Extract validate and build message property methods out of sendMessageActivity into a common util class so that it can be used by other modules.

### Describe the Solution You'd Like

Change method signatures from protected to public static and extract them into a common util class so that it can be used by other modules.

### Describe Alternatives You've Considered

No alternative.

### Additional Context

_No response_

Start by locating sendMessageActivity and its validate and build message property methods, then inspect how other modules could call them. Extract the methods into a common utility with public static signatures, update existing references, and run the relevant existing tests to verify behavior is unchanged.

Written by the indexing model from the issue text.