Fix Text Disappearing

[thecoolwinter]

Description

Fixes two small bugs:

• When deleting a line from the line text storage, a replaced node's left subtree metadata would be replaced, instead of added to when removing that node. This caused the left subtree to be invisible in some cases, leading to broken layout.
• Force a layout pass after editing, as was the behavior before the recent layout manager changes. Fixes an issue where editing text would not move the cursor correctly.
• Adds a test case to the aforementioned line storage bug.

Related Issues

• closes 🐞 Crash when deleting text CodeEditSourceEditor#196

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code

Screenshots

N/A