Allow accessing send queue count from WebSocketConnection

[Shane32]

Allows derived classes to check the send queue count and override SendMessageAsync in case the number of messages in the outbound queue is growing out of control. Perhaps in the future backpressure options will be available as a built-in feature.

[github-actions]

Coverage Report

Totals
Statements:	96.96% ( 1882 / 1941 )
Methods:	81.41% ( 289 / 355 )

[coveralls]

Pull Request Test Coverage Report for Build 11541026324

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 5 of 5 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.009%) to 94.537%

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Totals
Change from base Build 11540995157:	0.009%
Covered Lines:	1882
Relevant Lines:	1941

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💛 - Coveralls