Motion diff and line numbering performance

[bastianjoel]

This is a follow up to #3014 for preserving findings.

Problematic scenarios:

• a lot of amendments (50+) attached to a single motions
• amendments to very long motions

Affected pages:

• Motion detail
• Amendment list filtering
• Amendment list entry rendering

Identified performance bottlenecks

• line numbering calculation
• paragraph number calculation
• (getDiff calculation)

Besides from that we could discuss if it makes sense to introduce motion text size limits for which we display a warning.