LCP in Chrome considers text nodes which do not contain any content beyond whitespace

[andydavies]

https://issues.chromium.org/issues/403528013

(also https://issues.chromium.org/issues/40939328)

Demo: https://andydavies.github.io/agent-tests/lcp/rainbow.html

Firefox:

• Always the red square

Chrome:

• Desktop: red square
• Mobile: