fix: write docstring always

[lyt213]

Description

issue-2850306930 current: In VSCode, there is a function called "write a doc string" in the right-click menu, which passes a parameter "onlyOneInsertion" to streamEdit, which only allows receiving up to one line of duplicate content.

Problem: Except for the first line, all other content will be delete by function reapplyWithMyersDiff，cause by wrong range

fixed： when params onlyOneInsertion is true，set endrange = startrange

[ What changed? Feel free to be brief. ]

Checklist

• [x] I've read the contributing guide
• [x] The relevant docs, if any, have been updated or created
• [x] The relevant tests, if any, have been updated or created

Screenshots

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Tests

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