refactor(amazonq): combine IAM and SSO implementations of StreamingClientService

[liramon1]

Problem

The agentic bundle for the CodeWhisperer LSP only supports SSO. If language clients want it to consume IAM credentials, they must start a completely separate bundle which includes the IAM implementation of the CodeWhisperer LSP. This prevents clients from seamlessly switching authentication methods at runtime.

Solution

This is part of #1936.

This PR combines the IAM and SSO implementations of the StreamingClientService, which is a prerequisite for combining the IAM and SSO implementations of AmazonQServiceManager. References to StreamingClientServiceToken and StreamingClientServiceIAM will be changed in a later PR.

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 72.64151% with 522 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (liramon/flare-iam-base@99d2f70). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...nguage-server/agenticChat/agenticChatController.ts	54.63%	264 Missing ⚠️
...p-codewhisperer/src/shared/codeWhispererService.ts	37.07%	168 Missing ⚠️
chat-client/src/client/mynahUi.ts	17.39%	19 Missing ⚠️
...ge-server/inline-completion/codeWhispererServer.ts	56.09%	17 Missing and 1 partial ⚠️
...codewhisperer/src/shared/streamingClientService.ts	85.32%	16 Missing ⚠️
...-lsp-codewhisperer/src/shared/activeUserTracker.ts	93.19%	12 Missing and 1 partial ⚠️
...language-server/agenticChat/tools/chatDb/chatDb.ts	92.18%	10 Missing ⚠️
core/aws-lsp-core/src/util/processUtils.ts	80.76%	5 Missing ⚠️
...r/agenticChat/context/additionalContextProvider.ts	92.68%	3 Missing ⚠️
...r/agenticChat/context/agenticChatTriggerContext.ts	97.36%	1 Missing ⚠️
... and 5 more

Additional details and impacted files

@@                    Coverage Diff                    @@
##             liramon/flare-iam-base    #1959   +/-   ##
=========================================================
  Coverage                          ?   65.86%           
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  Files                             ?      238           
  Lines                             ?    50785           
  Branches                          ?     3401           
=========================================================
  Hits                              ?    33452           
  Misses                            ?    17273           
  Partials                          ?       60           

Flag	Coverage Δ
unittests	65.86% <72.64%> (?)

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