Provide AST count information without a separate visitor pass

[DavidHancu]

Describe the feature

When implementing a library that builds on top of SWC, we need to generate intermediary representations. This probably includes HashMaps or Vecs, which can benefit from a performance increase when initialized with the right capacity.

SWC should provide at least the following counts:

• node count (a count for all AST nodes)
• definition count (a count for all definitions, like functions and classes)
• export count (a count for all export specifiers)

Babel plugin or link to the feature description

No response

Additional context

This should not be implemented as a separate pass because it would be wasteful. This should be implemented at the parser level and I'm willing to contribute this.