How do I add java-psi-impl which contains JavaElementType to my plugin project?

I started a new intellij platform plugin project with gradle as it described in the documentation. My gradle.build looks like this (I haven't touched it since its creation):

plugins {
    id 'java'
    id 'org.jetbrains.intellij' version '0.4.15'
}

group 'com.github.neshkeev.functions'
version '0.0.0-SNAPSHOT'

sourceCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

// See https://github.com/JetBrains/gradle-intellij-plugin/
intellij {
    version '2019.3'
}
patchPluginXml {
    changeNotes """
      Add change notes here.<br>
      <em>most HTML tags may be used</em>"""
}

I need to add new entries for method references (e.g. Objects::toString) into CompletionResultSet, so I added a new CompletionContributor instance:

public class MethodReferenceCompletion extends CompletionContributor  {
    public MethodReferenceCompletion() {
        extend(
                CompletionType.BASIC,
                PlatformPatterns.psiElement(),
                new MethodReferenceCompletionProvider()
        );
    }
}

And new entries appears for all elements in the completion dialog. If I change the ElementPattern parameter to

PlatformPatterns.psiElement(/* method or ctor */).withParent(JavaElementType.METHOD_REF_EXPRESSION)

the compilation fails, because JavaElementType is not present on the classpath. I discovered that the class belongs to the java-psi-impl module, but it is not available on Maven Central, so I cannot forcibly add it to my build.gradle, how do I add the module?