Add package modifier

https://github.com/apple/swift-evolution/blob/main/proposals/0386-package-access-modifier.md

Author: taku0

swift-mode-font-lock.el

@@ -522,9 +522,9 @@ Return nil otherwise."
 
 (defconst swift-mode:declaration-keywords
   '("associatedtype" "class" "deinit" "enum" "extension" "fileprivate" "func"
-    "import" "init" "inout" "internal" "let" "open" "operator" "private"
-    "protocol" "public" "any" "some" "static" "struct" "subscript" "typealias"
-    "var" "actor" "nonisolated" "isolated" "distributed"
+    "import" "init" "inout" "internal" "let" "open" "operator" "package"
+    "private" "protocol" "public" "any" "some" "static" "struct" "subscript"
+    "typealias" "var" "actor" "nonisolated" "isolated" "distributed"
     "borrowing" "consuming")
   "Keywords used in declarations.")
 

swift-mode-lexer.el

@@ -669,7 +669,7 @@ return non-nil."
               '("indirect" "convenience" "dynamic" "final" "infix" "lazy"
                 "mutating" "nonmutating" "optional" "override" "postfix"
                 "prefix" "required" "static" "unowned" "weak" "internal"
-                "private" "public" "open" "fileprivate" "nonisolated"
+                "package" "private" "public" "open" "fileprivate" "nonisolated"
                 "distributed"))
       nil)
 
@@ -703,7 +703,7 @@ return non-nil."
               '("indirect" "convenience" "dynamic" "final" "infix" "lazy"
                 "mutating" "nonmutating" "optional" "override" "postfix"
                 "prefix" "required" "static" "unowned" "weak" "internal"
-                "private" "public" "open" "fileprivate" "nonisolated"
+                "package" "private" "public" "open" "fileprivate" "nonisolated"
                 "distributed"))
       t)
 

test/swift-files/indent/declarations.swift

@@ -760,6 +760,10 @@ class Foo {
       subscript(foo: Int) -> Int {
         return foo
     }
+
+    package
+      func foo() {
+    }
 }
 
 // async let

test/swift-files/indent/identifiers.swift

@@ -94,6 +94,9 @@ func foo() {
     foo(
       public: 1
     )
+    foo(
+      package: 1
+    )
     foo(
       static: 1
     )