Generate fake AST

[Rich-Harris]

Since Rollup can theoretically ingest an AST for a module, we might be able to do a clever hack here – this plugin could generate a fake AST that avoided the initial parse step and subsequent traversals. A similar optimisation could apply to e.g. rollup-plugin-string

[Rich-Harris]

Released this as 2.0.0. It's filthy, filthy code, but the gains are quite substantial in some cases – a colleague was inlining a few hundred kbs of geodata, and bundling time dropped ~10x.