BREAKING CHANGE: Refactor enum identifiers to TitleCase and apply some changes in AST nodes

[MaxGraey]

Changes:

• Canonicalize all enum identifiers from mixed (UPPER, UPPER_SNAKE and TitleCase) case to TitleCase only
• Rename statement to body in all loop-related AST nodes in ast.ts
• Rename statements to bodyStatements for TryStatement node in ast.ts
• Add Node > .isEmpty in ast.ts
• Add SwitchCase > .isDefault in ast.ts

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