chore: Move ArrowFlight to standard layout (#112)

## What's Changed

ArrowFlight has been moved to Sources/ArrowFlight
ArrowFlightTests has been moved to Tests/ArrowFlight
ArrowFlight/Package.swift has been deleted.
build.sh and lint config have been updated to reflect this structure.

Closes #78.

Author: willtemperley

.swiftlint.yml

@@ -16,12 +16,6 @@
 # under the License.
 
 included:
-  - Arrow/Package.swift
-  - Arrow/Sources
-  - Arrow/Tests
-  - ArrowFlight/Package.swift
-  - ArrowFlight/Sources
-  - ArrowFlight/Tests
   - CDataWGo/Package.swift
   - CDataWGo/Sources/go-swift
 excluded:
@@ -30,9 +24,9 @@ excluded:
   - Sources/Arrow/Schema_generated.swift
   - Sources/Arrow/SparseTensor_generated.swift
   - Sources/Arrow/Tensor_generated.swift
-  - ArrowFlight/Sources/ArrowFlight/Flight.grpc.swift
-  - ArrowFlight/Sources/ArrowFlight/Flight.pb.swift
-  - ArrowFlight/Sources/ArrowFlight/FlightSql.pb.swift
+  - Sources/ArrowFlight/Flight.grpc.swift
+  - Sources/ArrowFlight/Flight.pb.swift
+  - Sources/ArrowFlight/FlightSql.pb.swift
 identifier_name:
   min_length: 2 # only warning
 allow_zero_lintable_files: false

ArrowFlight/Package.resolved

@@ -60,7 +60,6 @@ let package = Package(
                 .product(name: "GRPC", package: "grpc-swift"),
                 .product(name: "SwiftProtobuf", package: "swift-protobuf")
             ],
-            path: "ArrowFlight/Sources/ArrowFlight",
             swiftSettings: [
                 // build: .unsafeFlags(["-warnings-as-errors"])
             ]
@@ -75,7 +74,6 @@ let package = Package(
         .testTarget(
             name: "ArrowFlightTests",
             dependencies: ["ArrowFlight"],
-            path: "ArrowFlight/Tests",
             swiftSettings: [
                 // build: .unsafeFlags(["-warnings-as-errors"])
             ]