Refresh indentation after user types in an empty template

[deepfuriya]

Description

Fixes indentation detection for templates that start empty. Previously, when a user opened a new empty
file and started typing with their preferred indentation (e.g., 2 spaces), the language server would use
the fallback tab size instead of detecting the user's actual indentation style.

Changes

• Added lazy indentation detection that re-evaluates when getTabSize() is called, allowing detection
  after content is added to an initially empty document
• Track whether indentation has been successfully detected to avoid redundant re-detection
• Pass detectIndentation setting through to getTabSize() to respect user preferences

Testing

• Added unit tests for Document indentation detection (lazy detection, fallback behavior, detection
  caching)
• Added unit tests for DocumentManager.getEditorSettingsForDocument() to validate VS Code settings
  integration
• Added E2E tests verifying snippet indentation matches user-typed indentation in completions

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