feat: Force UTF-8 encoding of input characters

[NicolasFR]

Description

Force UTF-8 encoding of input characters

Closes #926

Checklist:

• I have read the Contribution Guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

Contributor License Agreement

By submitting this pull request, I acknowledge and agree that my contributions will be included in Stirling-PDF and that they can be relicensed in the future under the MPL 2.0 (Mozilla Public License Version 2.0) license.

(This does not change the general open-source nature of Stirling-PDF, simply moving from one license to another license)

[Frooodle]

Were you able to test this?

[NicolasFR]

Yes, for example test file contain "This is a test with accents: é è à ç ù" with result is
test2.pdf