Duplicated messages in testdata appeared because default renderer
renders diagnostic spans ambiguously. It shows only start position.
In fact, there are 3 failures, 2 of them distinguish only by the
diagnostic end offset. See youtrack for more information.
The issue about inconvenient rendering is KT-64989.
#KT-64608
Before 5b7cee6221 JVM CLI compiler
was calling `KotlinToJVMBytecodeCompiler.compileBunchOfSources`.
`compileBunchOfSources` detected possible main classes,
and filled the Main-Class attribute in output jar
if if there was only one candidate.
After the change JVM CLI began calling
`KotlinToJVMBytecodeCompiler.compileModules`, which was not searching for a main class.
This change adds searching for main classes to `compileModules`.
We search for a main class only when one module is compiled,
and an output is written a jar file (so the change only affects JVM CLI compilation).
#KT-32272 Fixed
Evgeniy.Zhelenskiy