Issue Type: Performance Issue

Steps to reproduce

1. Open any text file with longer lines (more than 10k characters).
2. Try to edit the line (remove or add characters in between).

Observations

• The cursor movement is extremely slow and character updates take place after a long time.
• The same behaviour is observed when Word Wrap is on.
• Gives a warning sometimes

Tokenization is skipped for lines longer than 20k characters for performance reasons.

System Information

VS Code version: Code 1.25.1 (1dfc5e5, 2018-07-11T15:33:29.235Z)
OS version: Darwin x64 17.7.0