Display fragment mass with 2 decimal places

[jkraybill]

Summary

SUMMARY: Interface "Display fragment mass with 2 decimal places"

Purpose of change

Fixes #37614 to show 2 decimal places in fragment mass for explosives.

Describe the solution

Changed the code to format mass to 2 DP's instead of the current integer rounding. Now it looks like this:

Describe alternatives you've considered

1 decimal place or 3 decimal places; 2 DP's looked the most appropriate since I could find elements with 2 significant DP's but not 3.

Testing

Replicated the report in #37614 easily, then rebuilt and re-tested with the formatting code.

[Brian-Otten]

Thanks for tackling this, should help players understand how their explosives work a decent bit.