Minor cleanup on Extensions in Configuration

[maryamariyan]

Follow ups from older PRs. Checks off an item in #37821:

• Moves ConfigurationRootTest to common, used by two test projects (Microsoft.Extensions.Configuration: enabling FileExtensions/Ini #33844 (comment))

Using Invariant culture for remaining double params in EventSourceLoggerTest (#34208 (comment))

Related to: #39521 (removed commit ea24d1a)

cc: @tarekgh

Leaving EventSourceTest cleanup for later.

[ghost]

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[tarekgh]

 @"""ArgumentsJson"":{""timeParam"":""" + TimeParam.ToString() + @""",""guidParam"":""" + GuidParam.ToString("D")) },

does instances like this needed to be fixed tooo?

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Refers to: src/libraries/Microsoft.Extensions.Logging.EventSource/tests/EventSourceLoggerTest.cs:957 in bbf2215. [](commit_id = bbf221590519ca2d4f3331397fe2cee294bc85b2, deletion_comment = False)

[maryamariyan]

does instances like this needed to be fixed tooo?

I had and then reverted this commit ea24d1a from the PR (with this report: https://dev.azure.com/dnceng/public/_build/results?buildId=832928&view=ms.vss-test-web.build-test-results-tab&runId=26549100&resultId=102390&paneView=debug as it did not seem like a required change.)

e.g.:

Assert.Collection() Failure
\nCollection: ["{\"__EVENT_NAME\":\"MessageJson\",\"Level\":1,\"Fa"..., "{\"__EVENT_NAME\":\"MessageJson\",\"Level\":2,\"Fa"..., "{\"__EVENT_NAME\":\"ActivityJsonStart\",\"ID\":3,\"..., "{\"__EVENT_NAME\":\"MessageJson\",\"Level\":4,\"Fa"..., "{\"__EVENT_NAME\":\"MessageJson\",\"Level\":5,\"Fa"..., ...]\nError during comparison of item at index 5\nInner exception: Event data '{"__EVENT_NAME":"ActivityJsonStart","ID":4,"FactoryID":4,"LoggerName":"Logger3","ArgumentsJson":{"timeParam":"5/3/2016 7:00:00 PM","guidParam":"29bebd2c-7fa6-4e97-af68-b91fdaae24b6","{OriginalFormat}":"Inner scope {timeParam} {guidParam}"}}' does not contain expected fragment "ArgumentsJson":{"timeParam":"05/03/2016 19:00:00","guidParam":"29bebd2c-7fa6-4e97-af68-b91fdaae24b6
\n Expected: True\n Actual: False