Filter out invisible unicode characters from text segments

[JiuqingSong]

Summary

• Strip invisible Unicode tag characters (U+E0000–U+EFFFF) inside createText so they cannot survive paste/DOM-to-model conversion. These characters are used to hide instructions/text inside HTML (see https://embracethered.com/blog/posts/2024/hiding-and-finding-text-with-unicode-tags/) and otherwise leak into the model as normal text.
• Meaningful invisible characters that fall outside that range (e.g. ZWSP U+200B, ZWJ U+200D, RLO U+202E, PDF U+202C) are preserved.
• Unit tests in creatorsTest.ts cover mixed/boundary/only-invisible inputs and confirm meaningful invisible chars are untouched. An end-to-end test in endToEndTest.ts verifies a full DOM → Model → DOM/text round-trip strips only the tag range.

Test plan

• yarn test:fast --testPathPattern=creatorsTest
• yarn test:fast --testPathPattern=endToEndTest

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