Introduce readText and make stripUTF8BOM private

Introduce PackageName, to fully type a package name ...

Package names being passed around in the Dub codebase are string,
which is problematic as it suffers from validation / semantic issues.
Validation because we cannot impose restrictions on characters
or length easily, and semantic because some functions expect a main
package while some would accept a subpackage. Introducing a type
will remedy both those issues.

Trivial: Deprecate string overload of readPackageRecipe ...

To be consistent with the rest of Dub, use NativePath.

Move foreign code from global scope to dub.internal. ...

Avoids conflicting with the actual dub packages when working with dub as a library. Also, even if just by convention, it ensures that dependent code doesn't rely on this code as a public API.

Unify reading and writing files under a single API ...

This removes the range API and instead uses Appender,
while using a limited and centralized set of functions
to read/write from files.
The end goal is to permit dependency injection,
which is a pre-requisite to extending the test-suite.

Use configy library to parse dub.json file ...

This will provide a vastly superior UX to the users:
- They will be warned about typos;
- The type information provided will be more accurate and always include file/line infos
  (e.g. no more 'Invalid SemVer versions');
- We can expose a better recipe struct to library users on the long run,
  by separating the actual data DUB uses from what it reads;
- We can be more descriptive about errors / intent, for example by using `SetInfo`;

Fix missing sanitizing of subpackage targetTypes ...

A regression introduced in #2277.

Move fix for issue 711 outside of JSON/SDL parser ...

Having the fix for this issue in the parser means adding non-trivial logic.
It is easier to reason about to have this logic done as a post-processing step,
replacing the `autodetect` with the actually auto-detected version.
This also paves the way to have other `targetType` as default,
e.g. the `unittest` configuration should probably not be `library`.

Replace occurences of 'in ref' with 'const scope ref' ...

In support for dlang/dmd#11000

Rename Path to NativePath. ...

Matches the changes done in vibe.d 0.8.x and vibe-core.

USe a default package name for single file packages in case none is ...

provided

Rename parameter to match documentation.

Review dub.recipe.io and improve documentation.

Fix all deprecation warnings on 2.071.0-b1, except for std.stream. ...

std.stream is still needed to support UTF filenames.

Implement SDLang package recipe serialization.

Fix target type inheritance for configurations in the SDL recipe parser.

Compile fix.

Add package recipe I/O module.