Improved Handling of Multiple Separators in Environment Variable Parsing

[skanakal]

Summary

Fixes #13070

Occurred changes and/or fixed issues

handle multiple separators (: and =) in a line by finding the index of the first occurrence of either separator using a regular expression. After identifying the separator, we use the substring method to separate the key and value.

Technical notes summary

Areas or cases that should be tested

As mentioned in the issue repro steps.

Areas which could experience regressions

Screenshot/Video

Checklist

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[richard-cox]

This should be reviewed as part of the work for #12720