add $DPATH environment variable for file locations (#2281) ...

* error out on unknown environment variables

* add env + config for package + settings locations

fix #229

* adjust to review, extend $DPATH test

* review round 2

PackageManager.getBestPackage: Introduce Version[Range] overloads

Project: Use Dependency.visit instead of if/else

improve some output coloring ...

See #2347

Integrate Configy colored output with dub's

settings/selections: Only warn on unknown keys, add changelog ...

This will give users the time to adapt, without erroring right away.

Keep logging functionality out of the public API as requested in https://github.com/dlang/dub/pull/2124#issuecomment-813016939.

New logging module - initial functionality ...

The new module replaces dub.internal.vibecompat.core.log by using the
same function names, but implementing colored output and the left
fixed-width tag. Overloaded functions are provided to output colored
text.

Still missing initLogging() and non-TTY stdout/stderr detection

use json.get directly instead of casting ...

see https://github.com/dlang/dub/pull/2321/files#r928547114

Use Configy to read dub.selections.json

Move PlacementLocation from project to PackageManager ...

PlacementLocation define which local path is used for storing packages.
It has nothing to do with project (it's not even used there),
and should be contained inside PackageManager, even if currently
quite a few details are leaking all over the place.

Trivial: Streamline code when package not found in project ...

Instead of checking the same condition three times,
just do it one, and make it more obvious we're actually
handling different kind of Dependency.

Fix missing deserialization of fileVersion from dub.selections.json ...

A regression in master, which can lead to `dub upgrade` generating an
invalid dub.selections.json (with fileVersion = 0).

Deprecate duplicated JSON serialization for Dependency

Deprecate `PackageManager.loadSCMPackage` & other `Dependency`-related refactoring (#2312) ...

* Trivial: Take a nested function out of a foreach loop

* Deprecate PackageManager.loadSCMPackage's Dependency overload, use Repository

We're moving away from using `Dependency.m_range` to store the git ref,
and the `Repository` type has already been updated to include the information,
but some places still read it from `m_range`, including this one.

* Trivial: Forward Dependency's string ctor to VersionRange ctor

* Trivial: Simplify comparison with `VersionRange.Invalid` within `VersionRange`

SelectedVersions: Add Repository to overload set (#2314) ...

Before it was an independent function because it had a different set of parameters,
but now that it has been unified, we can put it in the overload set.
No deprecation since the previous change that deprecated selectVersionWithRepository
hasn't been released yet.

Various code simplification around `dub.selections.json` (#2311) ...

* Deprecate unused Json constructor

* Trivial: Fix import order in dub.project

* Simplify DependencyResolver filtering

DependencyResolver is only instantiated from one place, and never re-used.
It makes more sense to set those variables in the constructor,
and avoid repeatedly calling a single function.

* Move file format to dub.selections.json to its own struct

Our goal is to replace the handcrafted JSON code with configy.

Dependency: Move `spec` / git ref inside of `Repository` ...

The `Dependency` struct is logically acting as an `enum`,
with 3 discrete possibilities. However, some of the logic is
piggybacking on the (original) version logic.
`Repository` is one of them, and by separating things,
we can make stronger assumptions in `Version` and `Dependency`.

Make Project.addTestRunnerConfiguration() accept a const GeneratorSettings argument

getDefaultConfiguration(): Accept a const BuildPlatform argument ...

Like `Package.getDefaultConfiguration()` already does. Fixes a minor
annoyance for reggae.

[add BuildSettingsTemplate.dup() method instead]

Project.addTestRunnerConfiguration(): Don't accidentally modify base config's buildSettings ...

This most likely doesn't affect dub itself, as it only works with
a single configuration at a time. The problem has surfaced with reggae
though (which can use multiple dub configurations at a time) - the
`mainSourceFile` was removed from the base `application` config too.

Project: Remove dead m_packageSettings var and related func ...

git blame points to 2014, and it seems to be the ancestor of dub.selections.json

Fix dub_test_root imports for non-all-at-once compilations (#2288) ...

Which requires a regular `dub_test_root.d` filename *and* adding
the containing directory to the importPaths.

Make `dub describe -c unittest` auto-generate dub_test_root.d if required
Except with `--annotate` for a dry run.

Don't ignore targetName in non-executable unittest configurations

Build{Options,Requirements}: Use a common templated struct ...

A bit less copy-pasta is a small but appreciable win.

Don’t call writeln in generated code when measuring coverage and indent generated code

Refactor Dub.testProject() to Project.addTestRunnerConfiguration() ...

With some slight functional changes in Dub.testProject() - not
resetting m_project and creating the generator with the final
project.
And some minor log output changes.

Resolve WebFreak's comment about processVars empty

Change description of injectSourceFiles to inject-source-files ...

Co-authored-by: Jan Jurzitza <gh@webfreak.org>