_RenderDropdownMenuBody.computeDryLayout accesses this.constraints, but it should only access the constraints parameter passed into computeDryLayout. This PR removes this.constraints access.

Also, I removed a line in which the child's offset is being set in computeDryLayout. This appears to be an error:

Finally, I'm curious whether there is a reason why only the first child is being used to set the height?

Resolves#176494

Blocking#176494

Pre-launch Checklist

• I read theContributor Guide and followed the process outlined there for submitting PRs.
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• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with///).
• I added new tests to check the change I am making, or this PR istest-exempt.
• I followed thebreaking change policy and addedData Driven Fixes where supported.
• All existing and new tests are passing.

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