Flutter search index is 27MB on disk

[srawlins]

I just generated it, and it's 27MB. It is probably highly compressible, so maybe isn't a huge transfer cost. There are easy wins here:

• Remove overrides which do not have explicit docs.
• Create indexes. For example, an index of packageNames, and then each search item does not need to spell out its packageName. Additionally, each search item can be given an ID, and then the "enclosedBy" references can point to an ID.