[WIP] Ddoc: in-site (Ddox-like) search (chmgen version)

[wilzbach]

This is an initial experiment with using the symbols from chmgen for an in-site search.

Cons:

• JSON file is rather large (1.7M, 171K gzipped) - though the JSON file can be loaded lazily, s.t. this shouldn't have an impact
• no information about the symbol (class vs. struct, enum?, member?, field?)

See also: #2314

Todo:

• filter for duplicates?
• sort the results in a meaningful way
• generate a shortname for long names
• expand the name, e.g. std_regex#.splitter should be displayed as such not a just splitter

Example:

Chmgen:

Ddox's symbols:

[dlang-bot]

Thanks for your pull request, @wilzbach!

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[wilzbach]

Closing in favor of #2314 (using DDox's symbols)