Introduce -Xoutput-imports mode of JVM compiler

In this mode, instead of analyzing files and generating bytecode for
them, compiler just saves imports of each file in JSON map of form

'<path to file> -> [<import1>, <import2>, ...]'

It is needed for some external tools, notably for Google3 toolchain.

compiler/testData/cli/jvm/extraHelp.out

@@ -32,6 +32,7 @@ where advanced options include:
   -Xno-optimize              Disable optimizations
   -Xno-param-assertions      Don't generate not-null assertions on parameters of methods accessible from Java
   -Xno-receiver-assertions   Don't generate not-null assertion for extension receiver arguments of platform types
+  -Xoutput-imports=<path>    Output imports from all compiled files to the specified file in JSON format
   -Xscript-resolver-environment=<key=value[,]>
                              Script resolver environment in key-value pairs (the value could be quoted and escaped)
   -Xsingle-module            Combine modules for source files and binary dependencies into a single module

compiler/testData/cli/jvm/importsProducer.args

@@ -0,0 +1,4 @@
+$TESTDATA_DIR$/importsProducer
+-d
+$TEMP_DIR$
+-Xoutput-imports=$TESTDATA_DIR$/importsProducerDump.txt

compiler/testData/cli/jvm/importsProducer.out

@@ -0,0 +1 @@
+OK

compiler/testData/cli/jvm/importsProducer/a/A1.kt

@@ -0,0 +1,7 @@
+package a
+
+import c.JavaC
+
+class A1 {
+    val j: JavaC = JavaC()
+}

compiler/testData/cli/jvm/importsProducer/a/A2.kt

@@ -0,0 +1,5 @@
+package a
+
+class A2 {
+    val a1: A1? = null
+}

compiler/testData/cli/jvm/importsProducer/b/B1.kt

@@ -0,0 +1,10 @@
+package b
+
+import a.*
+
+class B1 {
+    companion object {
+        val a1: A1 = A1()
+        val a2: A2 = A2()
+    }
+}

compiler/testData/cli/jvm/importsProducer/b/nestedB/B2.kt

@@ -0,0 +1,7 @@
+package b.nestedB
+
+import a.A1 as AliasedA1
+import a.A1
+
+fun foo(x: AliasedA1): Int = TODO()
+fun bar(x: A1): Int = TODO()

compiler/testData/cli/jvm/importsProducer/c/C1.kt

@@ -0,0 +1,16 @@
+package c
+
+import a.A1
+import a.A2
+import b.B1.Companion.a2
+import b.nestedB.bar
+import b.nestedB.foo
+
+class C1 {
+    val x = foo(TODO())
+    val y = bar(TODO())
+
+    val z: A1? = null
+    val t: A2? = a2
+
+}

compiler/testData/cli/jvm/importsProducer/c/JavaC.java

@@ -0,0 +1,13 @@
+package c;
+
+import a.A1;
+import b.B1;
+import b.nestedB.B2Kt;
+
+public class JavaC {
+    private void doStuff() {
+        C1 c1 = new C1();
+        B1 b1 = new B1();
+        B2Kt.bar(new A1());
+    }
+}

compiler/testData/cli/jvm/importsProducerDump.txt

@@ -0,0 +1 @@
+{"\/home\/dsavvinov\/Repos\/kotlin-fork\/kotlin\/compiler\/testData\/cli\/jvm\/importsProducer\/a\/A1.kt":["import c.JavaC"],"\/home\/dsavvinov\/Repos\/kotlin-fork\/kotlin\/compiler\/testData\/cli\/jvm\/importsProducer\/a\/A2.kt":[],"\/home\/dsavvinov\/Repos\/kotlin-fork\/kotlin\/compiler\/testData\/cli\/jvm\/importsProducer\/b\/B1.kt":["import a.*"],"\/home\/dsavvinov\/Repos\/kotlin-fork\/kotlin\/compiler\/testData\/cli\/jvm\/importsProducer\/b\/nestedB\/B2.kt":["import a.A1 as AliasedA1","import a.A1"],"\/home\/dsavvinov\/Repos\/kotlin-fork\/kotlin\/compiler\/testData\/cli\/jvm\/importsProducer\/c\/C1.kt":["import a.A1","import a.A2","import b.B1.Companion.a2","import b.nestedB.bar","import b.nestedB.foo"]}