correct some mismatched names in docs

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What does the pull request do?

correct some mismatched names in docs.
there is some some difference between the demo code in docs and sample code.

Scope of this PR:

• fix or update to an existing sample
• add a new sample

What is the current behavior?

Checklist

If this is a new Sample

• Added a ReadMe-file
• Updated the landing page
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with a link to your sample in the related documentation page

In any case

• Spell-checking done
• Checked if all hyperlinks work
• Checked if all images are visible

Fixed issues