macos: add root-level .swiftlint.yml (#10890)

In order to support running from both the repository root and from
within Xcode project, and to keep things generally organized, our
primary .swiftlint.yml configuration file lives under macos/.

This change introduces a root-level .swiftlint.yml which limits the file
scope to macos/ and then includes macos/.swiftlint.yml for the rest of
the directives.

This unlocks a few benefits:

- We no longer need to pass an explicit `macos` path argument in any of
our invocations. SwiftLint will do the right thing when run either from
the repository root or from within the macos/ directory.
- It lets us easily exclude the macos/build/ directory (and re-enable
the 'deployment_target' rule). In the previous setup, this was more
challenging than you'd expect due to SwiftLint's path resolution rules
and required passing even more arguments like `--working-directory`.

The only downside is adding a new file to the repository root, but that
feels like the right trade-off given the benefits and conveniences.

macos/.swiftlint.yml

@@ -2,6 +2,9 @@
 #
 check_for_updates: false
 
+excluded:
+  - build
+
 disabled_rules:
   - cyclomatic_complexity
   - file_length
@@ -14,7 +17,6 @@ disabled_rules:
   - type_body_length
 
   # TODO
-  - deployment_target
   - for_where
   - force_cast
   - multiple_closures_with_trailing_closure

macos/Ghostty.xcodeproj/project.pbxproj

@@ -509,7 +509,7 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 			shellPath = /bin/sh;
-			shellScript = "[[ -z \"$GITHUB_ACTIONS\" ]] || exit 0;\n\nSWIFTLINT=\"\"\nif command -v swiftlint >/dev/null 2>&1; then\n    SWIFTLINT=\"$(command -v swiftlint)\"\nelif [[ -f \"/opt/homebrew/bin/swiftlint\" ]]; then\n    SWIFTLINT=\"/opt/homebrew/bin/swiftlint\"\nfi\n\nif [[ -n \"$SWIFTLINT\" ]]; then\n    \"$SWIFTLINT\" lint --quiet \"$SRCROOT\"\nfi\n";
+			shellScript = "[[ -z \"$GITHUB_ACTIONS\" ]] || exit 0;\n\nSWIFTLINT=\"\"\nif command -v swiftlint >/dev/null 2>&1; then\n    SWIFTLINT=\"$(command -v swiftlint)\"\nelif [[ -f \"/opt/homebrew/bin/swiftlint\" ]]; then\n    SWIFTLINT=\"/opt/homebrew/bin/swiftlint\"\nfi\n\nif [[ -n \"$SWIFTLINT\" ]]; then\n    \"$SWIFTLINT\" lint --quiet\nfi\n";
 			showEnvVarsInLog = 0;
 		};
 /* End PBXShellScriptBuildPhase section */