Removing need for RegEx when expanding ENV variables

[FracturedShader]

When starting up several programs with STATIC EDP on embedded hardware, this routine dominates the startup time due to the RegEx recompilation and std::regex internally being locale aware. Especially when the EDP XML is fairly large.

This work replaces the RegEx with a small finite state machine that does a single linear pass over the input. Results from perf show this significantly reduces parsing time (as all text of interest is passed through this method).

Description

Contributor Checklist

• Commit messages follow the project guidelines.
• The code follows the style guidelines of this project.
• Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A Any new/modified methods have been properly documented using Doxygen.
• N/A Any new configuration API has an equivalent XML API (with the corresponding XSD extension)
• Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• Changes are API compatible.
• N/A New feature has been added to the versions.md file (if applicable).
• N/A New feature has been documented/Current behavior is correctly described in the documentation.
• N/A Applicable backports have been included in the description.

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• Check CI results: failing tests are unrelated with the changes.