`named(name, action)` on monomorphic containers shouldn't require specifying a type

[eskatos]

Expected Behavior

plugins {
    java
}
sourceSets.named("test") {
    println(allJava)
}

Current Behavior

plugins {
    java
}
sourceSets.named("test") {
    println(allJava)    
}

* What went wrong:
Script compilation errors:

  Line 6:     println(allJava)
                      ^ Unresolved reference: allJava

Work around

plugins {
    java
}
sourceSets.named<SourceSet>("test") {
    println(allJava)
}

Your Environment

------------------------------------------------------------
Gradle 4.10
------------------------------------------------------------

Build time:   2018-08-27 18:35:06 UTC
Revision:     ee3751ed9f2034effc1f0072c2b2ee74b5dce67d

Kotlin DSL:   1.0-rc-3
Kotlin:       1.2.60
Groovy:       2.4.15
Ant:          Apache Ant(TM) version 1.9.11 compiled on March 23 2018
JVM:          9.0.4 (Oracle Corporation 9.0.4+11)
OS:           Mac OS X 10.13.4 x86_64

[eskatos]

Closing as fixed in #1116