codegen-java: Support not annotating constructor parameters (#792)

Motivation:
Spring Boot configuration classes neither require nor benefit from annotating constructor parameters with their name.
The same is true for pkl-config-java configuration classes compiled with `-parameter`.

Changes:
- Change CLI parameter `--params-annotation` to accept a `none` value.
  This is recommended in https://clig.dev/#arguments-and-flags and is how the `-F` parameter of the `ssh` command works.
- Change `paramsAnnotation` property in Gradle plugin, CliJavaCodeGeneratorOptions, and JavaCodegenOptions as follows:
  - Change meaning of `null` from "generate org.pkl.java.config.mapper.Named annotations" to "do not generate annotations".
    This is a breaking change (only) affecting users who explicitly set the property to `null` instead of omitting it.
  - Change property default from `null` to:
    `null` if `generateSpringBootConfig` is `true` and `org.pkl.java.config.mapper.Named` otherwise
- add tests
- update docs of this and other codegen options

Result:
Generated code does not contain unnecessary annotations.

docs/modules/pkl-gradle/partials/gradle-codegen-properties.adoc

@@ -36,6 +36,14 @@ Example: `generateSpringBootConfig = true` +
 Whether to generate config classes for use with Spring Boot.
 ====
 
+.implementSerializable: Property<Boolean>
+[%collapsible]
+====
+Default: `false` +
+Example: `implementSerializable = true` +
+Whether to generate classes that implement `java.io.Serializable`.
+====
+
 .renames: MapProperty<String, String>
 [%collapsible]
 ====
@@ -86,4 +94,3 @@ Keys in this mapping can be arbitrary strings, including an empty string.
 Values must be valid dot-separated fully qualifed class name prefixes, possibly terminated by a dot.
 ====
 
-// TODO: fixme (implementSerializable)