fix: use innerText when loading alphaTex from dom

[Danielku15]

Issues

Fixes #2330

Proposed changes

As the title says. I don't expect any major negative impact here. Rather currently we get some escaped entities.

In case of problems users can still opt to load the code via .tex()

Checklist

• I consent that this change becomes part of alphaTab under it's current or any future open source license
• Changes are implemented
• New tests were added

Further details

• This is a breaking change
• This change will require update of the documentation/website