AlphaTex Error improvements. Line/col numbers.

[jonaro00]

Issues

• Implements Add line and column number to AlphaTab errors #1044
• Adds more details and logic to display better error messages overall:
  • Add a specific error for when a string is opened but never closed before EOF.
  • Only show incorrect values of _syData when it makes sense.
  • lastValidSpot makes sure the error message points out where the incorrect syntax started instead of where the importer discovered the error.

Checklist

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

Further details

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

[jonaro00]

All 3 builds passing now :)

[Danielku15]

Thanks for the addition 😉