This implements support for wildcards in "exports".

• All tests are passing, including a quite robust one I added to builds/package-exports.ts
• Each ExportEntry can now potentially be mapped to multiple SourcePath objects. When an asterisk is detected in the outputPath, this uses glob to find all src files that match against the wildcard path (it runs a glob search for every distExtension in tryExtensions).
• There's virtually no functional changes to getExportEntries, I just cleaned up the parseExportsMap recursion logic a bit.
• My approach required passing an additional parameter into parseExportsMap. This method was accumulating a lot of parameters (it was up to four) so I merged them into a params object instead. I can flatten this out again if you prefer. The new interface I added is called ParseExportsContext.
• I changed fsExists to be synchronous and use existsSync (which isn't deprecated, unlike exists). For a CLI tool like this it's usually faster to keep things synchronous anyway, since Promises are just adding overhead and additional ticks. I can change this back too if you prefer.

I couldn't find a way to format the files according to a standard config, am I missing something?