Test large file tokenization/coloring optimization

[rebornix]

• anyOS @sbatten
• Linux @Tyriar

Complexity: 2

Testing #45944

When opening a file, we will show the top of the document or the last viewed portion of the document. For former case, we always see colorful content as we do some warmup (tokenize the top of the document) in advance. However for the later one, we sometimes see white code (in dark theme) first and then they become colorful as the tokenization is not super fast.

Our optimization here is tokenizing the viewport when opening the file by guessing the initial state of tokenization. So it can be wrong at the very beginning and get corrected after a while.

Testers you may want to verify

• The tokenization of the viewport can be wrong but when the whole tokenization process is done, all contents are in good state.
• Make sure contents after the viewport are tokenized finally.