Remove unsuported character by ggtext in Labels

[Felixmil]

• add utilitary function
• add unit test

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02% :tada:

Comparison is base (eec205f) 69.66% compared to head (2ba2497) 69.69%.

:exclamation: Current head 2ba2497 differs from pull request most recent head f9f9e82. Consider uploading reports for the commit f9f9e82 to get more accurate results

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #482 +/- ## =========================================== + Coverage 69.66% 69.69% +0.02% =========================================== Files 63 63 Lines 4262 4266 +4 =========================================== + Hits 2969 2973 +4 Misses 1293 1293 ``` | [Files Changed](https://app.codecov.io/gh/Open-Systems-Pharmacology/TLF-Library/pull/482?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-Systems-Pharmacology) | Coverage Δ | | |---|---|---| | [R/label.R](https://app.codecov.io/gh/Open-Systems-Pharmacology/TLF-Library/pull/482?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-Systems-Pharmacology#diff-Ui9sYWJlbC5S) | `100.00% <100.00%> (ø)` | | | [R/utilities-label.R](https://app.codecov.io/gh/Open-Systems-Pharmacology/TLF-Library/pull/482?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-Systems-Pharmacology#diff-Ui91dGlsaXRpZXMtbGFiZWwuUg==) | `100.00% <100.00%> (ø)` | |

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