Remove sync I/O from JsonValueUtils async write methods

[habbes]

Issues

This pull request fixes #2704 .

Description

The following async helper methods from JsonValueUtils had cases of synchronous I/O:

• WriteEscapedJsonStringAsync
• WriteEscapedCharArrayAsync
• WriteValueAsync(byte[])

Part of the reason was because the methods called other helper methods that performed synchronous TextWriter.Write calls. In such cases, I created true async versions of the affected methods.

The other reason was that the NonIndentedTextWriter did not override the async WriteAsync(char[] buffer, int index, int count) method. And the default implementation of TextWriter.WriteAsync(char[], int, int) calls the synchronous version. So I added an async override to the class.

Something else what pointing out is that because the internal StreamWriter is buffered, it would take a bunch of Write() calls before it actually flushes to the stream. This means that this issue would go undetected in many cases. To test this, I create a long payload to ensure that the StreamWriter actually flushes its content.

Checklist (Uncheck if it is not completed)

• Test cases added
• Build and test with one-click build and test script passed

Additional work necessary

If documentation update is needed, please add "Docs Needed" label to the issue and provide details about the required document change in the issue.

[xuzhg]

Is it safe to copyto the buffer with less size?

[habbes]

The amount to copy is determine by the substrLength. The caller of this method ensures that the substrLength is not greater than the buffer length: https://github.com/OData/odata.net/pull/2707/files#diff-c86855fdf1be1c1e0a820b8852ccc1fef825001c9ef74274af40778f7adfb96dR452.

Should we add an additional Debug.Assert in this method to check whether this precondition is violated?

Note that this method is a duplicate of the following existing method: https://github.com/OData/odata.net/pull/2707/files#diff-c86855fdf1be1c1e0a820b8852ccc1fef825001c9ef74274af40778f7adfb96dR780. The only change is that I replaced the ref parameters with Ref<int> so that we can use it in async methods.

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Total files changed: 4

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