Reduce string operation cost in VtEngine::PaintBufferLine

[skyline75489]

Summary of the Pull Request

References

PR Checklist

• Supports [Performance] vtebench tracking issue #10563
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
• Documentation updated. If checked, please file a pull request on our docs repo and link it here: #xxx
• Schema updated.
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[lhecker]

I'm not sure if I like this change much...
We could circumvent the entire performance overhead from the get-go by passing the entire console buffer line to this function. What it does now is splitting the console line into clusters, just to reassemble the line later on for VT. This feels very hacky to me and is what I would consider as the underlying issue.

[skyline75489]

Yeah I don’t like this, either. Will try something else later. 获取 Outlook for iOS<https://aka.ms/o0ukef>