Update modifiers related sections to be accurate to what we've been able to do since 3.25

[NullVoxPopuli]

This will

• [x] Update existing modifier language in the release docs
• [ ] once approved, I'll back port it all the way to 3.25
• [ ] removes mentions of @ember/render-modifiers as those modifiers were meant for migration from the old paradigms, and not exactly reflective of how the Octane mental model works.

Prior to 3.25, all modifiers had to be globally available in app/modifiers/* -- this is very awkward, and kind of unfortunate from a teaching perspective that we had such a big gap between modifiers being "the thing" and when they can be freely used -- so I'll be ignoring everything prior to 3.25 for these updates.

[jenweber]

I made some small wording changes, added a label to the pre-existing input example, and added eager: false to address a deprecation warning. I tested this example and I think it's good to go. Would anyone else like to review before we merge? @ember-learn/learning-core-team

[NullVoxPopuli]

hmm eager: false "feels temporary". :thinking: @chriskrycho -- any feels as to when ember-modifier v4 is happening? <3

[NullVoxPopuli]

I just found -- guides/release/upgrading/current-edition/glimmer-components.md / https://guides.emberjs.com/release/upgrading/current-edition/glimmer-components/

I'm gonna address in a separate PR once we resolve this one :partying_face: