fix: avoid placeholder reuse on content change

[Danielku15]

Issues

Fixes #2488

Proposed changes

We now avoid reusing the viewport in cases where we detect that the content has changed significantly. This avoids partials keeping their content causing weird/wrong notation being shown when having a larger re-rendering.

e.g. when switching between layouts the content of the partials has to be cleared. Same when the whole rendered score changes.

In cases where the developer knows the score should be same/similar, a new RenderingHints object specifying that the viewport should be reused. This provides a better experience when doing live-editing.

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