enh(scala) add using soft keyword

`using` is a keyword if it appears at the start of a parameter or argument list.
See https://docs.scala-lang.org/scala3/reference/soft-modifier.html

Based on https://github.com/scala/vscode-scala-syntax/blob/57e0829cd46980699570101a68c320a20330d36c/src/typescript/Scala.tmLanguage.ts#L504

CHANGES.md

@@ -16,6 +16,7 @@ Grammars:
 - enh(css/less/stylus/scss) add support for CSS Grid properties [monochromer][]
 - enh(java) add support for Java Text Block (#3322) [Teletha][]
 - enh(scala) add missing `do` and `then` keyword (#3323) [Nicolas Stucki][]
+- enh(scala) add `using` soft keyword (#3330) [Nicolas Stucki][]
 
 [Austin Schick]: https://github.com/austin-schick
 [Josh Goebel]: https://github.com/joshgoebel

src/languages/scala.js

@@ -117,6 +117,11 @@ export default function(hljs) {
     contains: [ NAME ]
   };
 
+  const USING_PARAM_CLAUSE = {
+    className: 'keyword',
+    begin: /(?<=\(\s*)using(?=\s(?!\s*\)))/,
+  };
+
   return {
     name: 'Scala',
     keywords: {
@@ -132,6 +137,7 @@ export default function(hljs) {
       METHOD,
       CLASS,
       hljs.C_NUMBER_MODE,
+      USING_PARAM_CLAUSE,
       ANNOTATION
     ]
   };

test/markup/scala/using.expect.txt

@@ -0,0 +1,11 @@
+<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span></span>(<span class="hljs-keyword">using</span> x: <span class="hljs-type">Int</span>) = <span class="hljs-number">1</span>
+<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">g</span></span>(<span class="hljs-keyword">using</span> <span class="hljs-type">Int</span>) = <span class="hljs-number">1</span>
+given (<span class="hljs-keyword">using</span> ev: <span class="hljs-type">Ev</span>): <span class="hljs-type">Foo</span> = ???
+
+<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">expressions</span> </span>=
+  f(<span class="hljs-keyword">using</span> <span class="hljs-number">2</span>)
+
+  <span class="hljs-comment">// not `using` keyword</span>
+  (using)
+  (using )
+  ( using )

test/markup/scala/using.txt

@@ -0,0 +1,11 @@
+def f(using x: Int) = 1
+def g(using Int) = 1
+given (using ev: Ev): Foo = ???
+
+def expressions =
+  f(using 2)
+
+  // not `using` keyword
+  (using)
+  (using )
+  ( using )