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.

Author: Geod24

source/dub/dub.d

@@ -825,7 +825,7 @@ class Dub {
 		}
 
 		// always upgrade branch based versions - TODO: actually check if there is a new commit available
-		Package existing = m_packageManager.getPackage(packageId, ver, placement);
+		Package existing = m_packageManager.getPackage(packageId, ver, location);
 		if (options & FetchOptions.printOnly) {
 			if (existing && existing.version_ != ver)
 				logInfo("A new version for %s is available (%s -> %s). Run \"%s\" to switch.",
@@ -863,7 +863,7 @@ class Dub {
 		if (dstpath.existsFile())
 		{
 			m_packageManager.refresh(false);
-			return m_packageManager.getPackage(packageId, ver, dstpath);
+			return m_packageManager.getPackage(packageId, ver, location);
 		}
 
 		// repeat download on corrupted zips, see #1336

source/dub/packagemanager.d

@@ -195,6 +195,7 @@ class PackageManager {
 	}
 
 	/// ditto
+	deprecated("Use the overload that takes a `PlacementLocation`")
 	Package getPackage(string name, Version ver, NativePath path)
 	{
 		foreach (p; getPackageIterator(name)) {
@@ -205,6 +206,15 @@ class PackageManager {
 		return null;
 	}
 
+	/// Ditto
+	Package getPackage(string name, Version ver, PlacementLocation loc)
+	{
+		// Bare mode
+		if (loc >= this.m_repositories.length)
+			return null;
+		return this.m_repositories[loc].lookup(name, ver);
+	}
+
 	/// ditto
 	deprecated("Use the overload that accepts a `Version` as second argument")
 	Package getPackage(string name, string ver, NativePath path)
@@ -1175,6 +1185,30 @@ private struct Location {
 			logDiagnostic("Failed to enumerate %s packages: %s", path.toNativeString(), e.toString());
 	}
 
+	/**
+	 * Looks up already-loaded packages at a specific version
+	 *
+	 * Looks up a package according to this `Location`'s priority,
+	 * that is, packages from the search path and local packages
+	 * have the highest priority.
+	 *
+	 * Params:
+	 *	 name = The full name of the package to look up
+	 *	 ver  = The version to look up
+	 *
+	 * Returns:
+	 *	 A `Package` if one was found, `null` if none exists.
+	 */
+	private inout(Package) lookup(string name, Version ver) inout {
+		foreach (pkg; this.localPackages)
+			if (pkg.name == name && pkg.version_.matches(ver, VersionMatchMode.strict))
+				return pkg;
+		foreach (pkg; this.fromPath)
+			if (pkg.name == name && pkg.version_.matches(ver, VersionMatchMode.strict))
+				return pkg;
+		return null;
+	}
+
 	/**
 	 * Get the final destination a specific package needs to be stored in.
 	 *