TypeScript shrinks AST node header from 48 to 32 bytes

The TypeScript compiler now embeds the node header directly at offset zero inside concrete AST node structures. The header shrank from 48 to 32 bytes, cutting memory footprint and garbage collection overhead, with gains measured in VS Code.

• AST node header reduced from 48 to 32 bytes
• Header embedded at offset zero in each node
• Lower memory use and GC scanning overhead
• Improvements measured in VS Code