Inline imports redivivus

[Andrei Alexandrescu]

On 7/23/21 9:55 AM, Andrei Alexandrescu wrote:
> Mathias Lang just told me the bug preventing inline imports from working 
> has been fixed, so I reopened this:
> 
> https://github.com/dlang/druntime/pull/1756
> 
> I think it's a very useful facility, more clearly so for large projects, 
> and deserves a fair shake of the stick.
> 
> If it works well in practice, a future language proposal could take 
> `_import!"std.datetime".SysTime` to the simpler and better 
> `import(std.datetime).SysTime`. Using it as a library facility seems 
> like a good step.

Per our coding standards I renamed `_import` to `import_` although I 
find the latter awfully bizarre.