Update HttpRequestMessageFactory to correctly set the Content-Length header

[muhammad-othman]

Description

This PR updates the .NET Standard implementation of the HttpRequestMessageFactory to correctly set the Content-Length header, particularly for non-seekable streams, by taking the current stream position into account.

The issue being addressed was originally fixed in #3631. However, due to the test coverage only verifying behavior when UseChunkEncoding = false, the regression was reintroduced when the position adjustment was moved behind a check that only applies to seekable streams.

This update ensures that the stream position is correctly accounted for when setting Content-Length, regardless of the stream's seekability.

Motivation and Context

#3629

Testing

• DRY_RUN-05ce4689-5754-4c4b-afd9-b0119f943459.
• Updated TestResetStreamPosition test to run with and without ChunkEncoding.

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[niemyjski]

Looks good, thanks for tracking this down.

[normj]

nit: Not relying on the CanSeek is due to special circumstances of our ChunkedUploadWrapperStream. You might want to add a comment here so somebody in the future, like myself, don't suggest adding back the CanSeek check to avoid the control flow by exception.