PackMan: Deprecate overload leaking location path ...

Currently, a lot of the internals of the PackageManager are leaking.
The getPackage overload accepting both a version and a NativePath
is an example of such a leak, and looking at the usage sites
show that things can be simplified by taking a PlacementLocation,
which is a higher level representation of the path.

Move PackageManager.getPackagePath to Location ...

It is more suited as a Location method, as it returns a path based on PackagePath.
This also allows us to reduce the leak of information about Location
happening in dub.

Deprecate PackageManager.completeSearchPath ...

It is no longer used within the PackageManager and leaks quite a bit of the internals,
instead users should have functionalities exposed via the PackageManager's API.

Deprecate an unused PackageManager.getPackage ovrld ...

This overload is not used anywhere in `dub`, and its use case is not clear.
Path where packages are stored should ideally be only known to `PackageManager`,
and the API should expose `PlacementLocation` instead of bare `NativePath`.
With this in mind, this overload doesn't fit the picture.

Deprecate PackageManager.getFirstPackage ...

This function returns the 'first' package, which is very arbitrary.
Instead, always return the highest matching package for stable results.

PackageManager: Simplify removeLocalPackage by using algorithm ...

Instead of doing (potentially) multiple append operations of two slices,
just do a filter + array which is much easier to read and prove correct.

PackageManager: Remove m_disableDefaultSearchPath, use array instead ...

The boolean is redundant, as the array will always be null / empty
if it's true, and have 3 entries otherwise.

Trivial: Improve PackageManager.m_repositories documentation

Remove PackageManager deprecations from v1.20.0 ...

Those deprecations have been introduced in v1.20.0,
so if we follow the same 10 releases policy as DMD,
we are good to have them removed in the next release.
Deprecated in 48a26db

PackageManager: Make internal scope have the priority, remove m_temporaryPackages ...

Before, `m_internal.fromPath` was unused, and `m_internal.localPackages` was only
used for the bare mode search paths, while a similar array of packages named
`m_temporaryPackages` was used for `Repository` / `NativePath` dependencies.

In both cases, this array should have priority over the other scopes,
so we can just remove the duplication and swap the iteration order.

PackageManager: Move the scanning logic to Location, segment per Location ...

Before this change, all packages were surprisingly stored in m_internal.localPackages,
which itself is a new addition to replace an array of 'Package'.
This means that even though we had an architecture that looks like it segmented
things per repository / location, it actually didn't,
and things worked solely based on the order packages were added it
(and the fact we did a linear search).

PackageManager.Location: Split packages registered locally and read from path ...

A Location, having a default search path (the package path),
and some extra search path, optionally, previously stored
all of them in the same array. However, this creates problems,
as we want to move to lazy load the packages in the default
search path, while we can't lazy load packages in non-default ones.

Trivial: Fix some style issues

PackageManager: Simplify logic around refreshing packages ...

Passing an empty array will lead to the same behavior
as using a boolean, so we can remove the parameter.

Trivial: Rename refresh_existing_packages parameter to refresh

Trivial: Reduce noise and allocation while reading local-packages.json

Trivial: Improve dub.packagemanager : Location documentation

Deprecate overrides: local-overrides.json, add-override, remove-override ...

As explained in the changelog, overrides were a solution to a system
with version-only dependencies, which is long gone.

PackageManager: Move scanPackageFolder to Location ...

A simple move for now to keep it simple,
the breach of abstraction will be resolved in a latter commit.

PackageManager.scanPackageFolder: Do some cosmetic fixes

PackageManager: Move class' extra searchPath/Package to an internal location ...

Those fields have been aggregated in Location and them being in `PackageManager`
stands out as a double duty (the `PackageManager` is both a `Location`
and act as a `Location` manager). By using a `Location` for them we can
start to streamline the code.

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`;

Trivial: Convert some spaces to tabs

PackageManager: Deprecate overloads of getPackage with string version

Call file.isDir once in hashPackage

Use SHA256 and better namings in hashPackage

PackageManager.getBestPackage: Introduce Version[Range] overloads

PackageManager: Move routine to write local pkg list to Location struct

PackageManager: Move routine to write override in Location struct

Trivial: Remove redundant cast