Add Gson dependency and module requirement

* Add `requires com.google.gson` to `module-info.java`
* Add Gson library entry to `libs.versions.toml`
* Add Gson dependency to `dependencies` section in `build.gradle`

annotations/src/main/java/module-info.java

@@ -4,4 +4,6 @@
     // This way we can still use the internal package, but not
     // to external developers.
     exports org.spongepowered.eventgen.annotations.internal to org.spongepowered.eventimplgen;
-}
+
+    requires com.google.gson;
+}

build.gradle

@@ -109,6 +109,8 @@ dependencies {
 
     compileOnlyApi libs.jetbrainsAnnotations
 
+    api(libs.gson)
+
     // Tests
     testImplementation libs.assertj
     testImplementation libs.joor
@@ -119,4 +121,4 @@ dependencies {
     testImplementation libs.junit.params
     testRuntimeOnly libs.junit.engine
     testRuntimeOnly libs.junit.launcher
-}
+}

gradle/libs.versions.toml

@@ -7,6 +7,7 @@ checkerQual = "3.26.0"
 dagger = "2.52"
 errorprone = "2.28.0"
 junit = "5.10.2"
+gson = "2.8.8"
 
 [libraries]
 autoService-annotations = { module = "com.google.auto.service:auto-service-annotations", version.ref = "autoService" }
@@ -19,6 +20,7 @@ javapoet = { module = "io.soabase.java-composer:java-composer", version = "1.0"
 jetbrainsAnnotations = { module = "org.jetbrains:annotations", version = "24.1.0"}
 jakartaInject = { module = "jakarta.inject:jakarta.inject-api", version = "2.0.1" }
 javaxInject = { module = "javax.inject:javax.inject", version = "1" }
+gson = { module = "com.google.code.gson:gson", version.ref = "gson" }
 
 # Tests
 assertj = { module = "org.assertj:assertj-core", version = "3.26.0" }