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-gradle/pkl-gradle.gradle.kts

@@ -12,9 +12,9 @@ plugins {
 }
 
 dependencies {
-  // Declare a `compileOnly` dependency on `project(":pkl-tools")`
+  // Declare a `compileOnly` dependency on `projects.pklTools`
   // to ensure correct code navigation in IntelliJ.
-  compileOnly(project(":pkl-tools"))
+  compileOnly(projects.pklTools)
 
   // Declare a `runtimeOnly` dependency on `project(":pkl-tools", "fatJar")`
   // to ensure that the published plugin 
@@ -31,7 +31,7 @@ dependencies {
     runtimeOnly(project(":pkl-tools", "fatJar"))
   }
 
-  testImplementation(project(":pkl-commons-test"))
+  testImplementation(projects.pklCommonsTest)
 }
 
 publishing {