Add javac plugin for detecting common error cases at compile time (#8196)

Adds a `@NoDiscard` annotation that can be placed on methods to guarantee their return values are used and on types to guarantee that any method returning that type uses the return value.

Methods that call `@NoDiscard`-annotated functions can add a `@SuppressWarnings("NoDiscard")` or `@SuppressWarnings("all")` annotation (or annotation on the class declaring that method) to silence the compiler error warnings.

docs/build.gradle

@@ -9,6 +9,7 @@ evaluationDependsOn(':cscore')
 evaluationDependsOn(':epilogue-runtime')
 evaluationDependsOn(':hal')
 evaluationDependsOn(':ntcore')
+evaluationDependsOn(':wpiannotations')
 evaluationDependsOn(':wpilibNewCommands')
 evaluationDependsOn(':wpilibc')
 evaluationDependsOn(':wpilibj')
@@ -174,6 +175,7 @@ task generateJavaDocs(type: Javadoc) {
     source project(':epilogue-runtime').sourceSets.main.java
     source project(':hal').sourceSets.main.java
     source project(':ntcore').sourceSets.main.java
+    source project(':wpiannotations').sourceSets.main.java
     source project(':wpilibNewCommands').sourceSets.main.java
     source project(':wpilibj').sourceSets.main.java
     source project(':wpimath').sourceSets.main.java