fix: respect HTML constraints for remote forms

[RazinShafayet2007]

Fixes #15270

This fixes remote forms so minlength and maxlength are respected during submission, preventing the remote POST request from being sent when a user-entered value is invalid. The change also applies the same HTML length-constraint handling to validate({ preflightOnly: true }) for dirty user-edited fields, while avoiding false positives for values set programmatically through fields.set(...). It also preserves browser-native validation messaging and adds regression coverage for the original repro, preflight validation, and rogrammatic value updates.

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