Use Gradle typed project accessors

This change activates the `TYPESAFE_PROJECT_ACCESSORS` feature
preview in Gradle, and switches to such accessors instead of
string-based project references, where possible

Relates-To: apple/pkl#204
Signed-off-by: Sam Gammon <sam@elide.ventures>

pkl-config-java/pkl-config-java.gradle.kts

@@ -62,7 +62,7 @@ sourceSets.getByName("test") {
 
 dependencies {
   // "api" because ConfigEvaluator extends Evaluator
-  api(project(":pkl-core"))
+  api(projects.pklCore)
 
   implementation(libs.geantyref)
 
@@ -70,7 +70,7 @@ dependencies {
 
   firstPartySourcesJars(project(":pkl-core", "sourcesJar"))
 
-  pklCodegenJava(project(":pkl-codegen-java"))
+  pklCodegenJava(projects.pklCodegenJava)
 }
 
 tasks.shadowJar {