[Teams] Add support for meeting participants added/removed events

[ceciliaavila]

#minor

Description

This PR is based on #5809. It adds support to TeamsActivityHandler for meeting participant join/leave events.

Specific Changes

• Added support for 2 new activity types - application/vnd.microsoft.meetingParticipantJoin and application/vnd.microsoft.meetingParticipantLeave.
• Added functions to register handlers for when teams meeting participants are joined/left.
• Added unit tests.

Testing

These images show the new unit tests passing and the implementation tested with a sample.

[coveralls]

Pull Request Test Coverage Report for Build 364374

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 27 unchanged lines in 7 files lost coverage.
• Overall coverage decreased (-0.006%) to 78.977%

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Files with Coverage Reduction	New Missed Lines	%
/libraries/AdaptiveExpressions/BuiltinFunctions/GetNextViableDate.cs	1	90.91%
/libraries/AdaptiveExpressions/BuiltinFunctions/GetPreviousViableDate.cs	1	93.94%
/libraries/integration/Microsoft.Bot.Builder.Integration.AspNet.Core/ServiceCollectionExtensions.cs	1	93.55%
/libraries/Microsoft.Bot.Connector.Streaming/Transport/TransportHandler.cs	2	96.39%
/libraries/Microsoft.Bot.Builder/Teams/TeamsActivityHandler.cs	6	79.35%
/libraries/Microsoft.Bot.Connector.Streaming/Session/StreamingSession.cs	6	89.62%
/libraries/Microsoft.Bot.Builder.Dialogs.Declarative/Converters/InterfaceConverter.cs	10	81.16%

Totals
Change from base Build 362013:	-0.006%
Covered Lines:	25959
Relevant Lines:	32869

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💛 - Coveralls

[ceciliaavila]

Hi @tracyboehrer, there's a problem with the CI pipeline in this PR. We think is related to the custom Nuget feed.
Please, let us know if we can help solve this.
Thanks.

[BruceHaley]

✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.dll
✔️ No Binary Compatibility issues for Microsoft.Bot.Schema.dll