Handle time zone environment variable having international characters.

[jonsimantov]

Description

Provide details of the change, and generalize the change in the PR title above.

Avoid sending the backend the wrong time zone format (or one with international characters) by using the Windows ICU library to get the canonical IANA time zone names (e.g. "America/Los Angeles").

Previously, on Windows, it used the "TZ" environment variable verbatim. This could have contained international characters (see #869). Now, use _tzset() to get the canonical Windows name, and then use the ICU library to convert it to the IANA name, which the Remote Config backend expects.

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Testing

Describe how you've tested these changes. Link any manually triggered Integration tests or CPP binary SDK Packaging Github Action workflows, if applicable.

Tested with "Romance Standard Time" --> "Europe/Paris" with LogInfo, prior to changing back to LogDebug.

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Type of Change

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• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• Other, such as a build process or documentation change.

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Notes

• Bug fixes and feature changes require an update to the Release Notes section of release_build_files/readme.md.
• Read the contribution guidelines CONTRIBUTING.md.
• Changes to the public API require an internal API review. If you'd like to help us make Firebase APIs better, please propose your change in a feature request so that we can discuss it together.

[github-actions]

Integration test with FLAKINESS (succeeded after retry)

Requested by @jonsimantov on commit 974fb07
Last updated: Thu Jun 1 19:16 PDT 2023
View integration test log & download artifacts

Failures	Configs
app_check	[TEST] [FLAKINESS] [Android] [1/3 os: ubuntu] [1/2 android_device: android_target] (1 failed tests)   FirebaseAppCheckTest.TestDebugProviderValidToken
firestore	[TEST] [FLAKINESS] [Android] [1/3 os: windows] [1/2 android_device: android_target] (1 failed tests)   CRASH/TIMEOUT

Add flaky tests to go/fpl-cpp-flake-tracker

[jonsimantov]

FYI not planning to merge until after the Unity release, just to be safe.

[jonsimantov]

Unity build and tests succeeded here: https://github.com/firebase/firebase-unity-sdk/actions/runs/5138069241

[jonsimantov]

Removed the extraneous log statements and added a comment to the cmake file.