Block comments.

test/comment_block.wren

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+// In middle of line.
+io.write/* ... */(/* */"ok"/* */) // expect: ok
+
+// Nested.
+io.write(/* in /* nest */ out */"ok") // expect: ok

test/comment_block_at_eof.wren

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+io.write("ok") // expect: ok
+/* comment */

test/comment_line_at_eof.wren

@@ -0,0 +1,2 @@
+io.write("ok") // expect: ok
+// comment