Send Standalone LCP spans

[Lms24]

Problem Statement

TLDR: Our current LCP collection approach suffers some limitations and accuracy suffers because the measurment duration is tied to the lifetime of the pageload span.

Solution Brainstorm

By decoupling LCP collection from the pageload span, we should get more accurate LCP values that more closely align with other web vital measuring tools. We'll introduce this as an experimental option first and check it on the Sentry project.