[Security Solution] Threat mapping overflows in rule upgrade flyout on narrow screens

[maximpn]

Epic: #174168
Relates to: #200308

Summary

Threat match rules may have threat mapping input overflowing rule upgrade flyout on narrow screens.

Steps to reproduce

• Have a threat match rule to upgrade (see [Security Solution] Add Threat Match rule specific editable fields #200308 for env preparation details)
• Make sure threat match mapping is show in rule upgrade flyout
• Make the screen narrower, e.g. 1024px wide

ER: Threat match mapping inputs are shown without overflow.
AR: Threat match mapping inputs overflow the screen and make the Diff View side narrower.

Screenshots:

[elasticmachine]

Pinging @elastic/security-detections-response (Team:Detections and Resp)

[elasticmachine]

Pinging @elastic/security-detection-rule-management (Team:Detection Rule Management)

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)