fix: Convert paths to POSIX paths before checking in esbuild handling logic

[lucashuy]

Why is this change necessary?

Windows paths contain an escape backslash (\\). This needs to be turned into a POSIX path before being parsed/saved into the template file.

How does it address the issue?

Makes sure that the string path from the helper method is a POSIX path (/ instead of \\) before parsing.

What side effects does this change have?

None.

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.