Helper to resolve dart version for clients of analytics

[eliasyishak]

This PR provides a helper method that can be used by clients of package:unified_analytics to resolve the dart sdk version from the Platform.version string provided by dart:io.

Additional parsing is necessary because we want to remove the extra information that is returned from this string.

Original from Platform.version: 3.3.0 (stable) (Tue Feb 13 10:25:19 2024 +0000) on "macos_arm64"

After parsing with helper:      3.3.0

The above is for dart sdks on the stable channel, the below is for non-stable

Original from Platform.version: 2.1.0-dev.8.0.flutter-312ae32

After parsing with helper:      2.1.0 (build 2.1.0-dev.8.0 312ae32)

The logic for this regex was borrowed from the logic that exists within the flutter/flutter repo

https://github.com/flutter/flutter/blob/stable/packages/flutter_tools/lib/src/cache.dart#L410-L423

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[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:unified_analytics	5.8.2	ready to publish	unified_analytics-v5.8.2
package:cli_config	0.1.2	already published at pub.dev
package:extension_discovery	2.0.1-wip	WIP (no publish necessary)
package:graphs	2.3.2-wip	WIP (no publish necessary)

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.