Consider deprecating Moment.js due to it being legacy tech

[mor10]

Description

Moment.js is considered a legacy project by its maintainers:

"We now generally consider Moment to be a legacy project in maintenance mode. It is not dead, but it is indeed done."

Source: https://momentjs.com/docs/

Apart from the various issues with Moment.js itself, JS itself now encapsulates much if not all its features.

Recommendations

• Deprecate Moment.js and replace with standard JS features.
• Update documentation to provide adequate transition instructions for devs using Moment.js features.

History of this discussion

This is a copy of #27859 which was closed because it was part of the discussion in #15277. The last mention of Moment in that thread was a misunderstanding about its role in the build process. The thread was moved to discussion #30976 but there is no clarity there as to the future of Moment in Gatsby. My request for clarity resulted in an instruction to open a new discussion, so here we are.