language: add comment token for java files (helix-editor#12266)

Author: TornaxO7

languages.toml

@@ -1183,6 +1183,7 @@ file-types = ["java", "jav", "pde"]
 roots = ["pom.xml", "build.gradle", "build.gradle.kts"]
 language-servers = [ "jdtls" ]
 indent = { tab-width = 2, unit = "  " }
+comment-token = "//"
 
 [[grammar]]
 name = "java"