Fix textarea content rendered twice

[jmerle]

Description

This PR fixes #50, i.e. content in textareas being rendered twice. This appears to be caused by copyInputValue copying the original textarea's value into the clone textarea's innerHTML, after which the cloneChildNodes call in src/clone-node.ts:223 appends clones of the textarea's child nodes to the same innerHTML. This effectively repeats what copyInputValue already did, resulting in the original content appearing twice in the clone. I fixed the issue by removing the copying that happens in copyInputValue.

Before:

After:

Additional context

The font rendering on my system is slightly different from the one used to generate the test fixture images, so I did not add a unit test because it'll likely fail on the system that was used to generate the existing fixtures.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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