[K2] Avoid shortening duplicated PSI elements

The existing K2 reference shortener collects all the PSI elements to
shorten. As a result, it possibly shortens duplicated PSI elements. For
example,
```
// FILE: main.kt
package a.b.c

fun test(n: Int) {
    return if (<expr>x.y.z.Outer.Inner.VALUE0 > x.y.z.Outer.Inner.VALUE1</expr>) 1
    else n
}
// FILE: values.kt
package x.y.z

class Outer {
    object Inner {
        val VALUE0 = 13
        val VALUE1 = 17
    }
}
```
for the above code, the existing K2 reference shortener tried to shorten
- x.y.z.Outer.Inner -> Inner
- x.y.z.Outer.Inner.VALUE0 -> VALUE0
- x.y.z.Outer.Inner -> Inner
- x.y.z.Outer.Inner.VALUE1 -> VALUE1

`x.y.z.Outer.Inner` is included in the list to shorten twice.
When it actually shortens the PSI elements, it shortens only
- x.y.z.Outer.Inner.VALUE0 -> VALUE0
- x.y.z.Outer.Inner.VALUE1 -> VALUE1

but it imports all of
- x.y.z.Outer.Inner
- x.y.z.Outer.Inner.VALUE0
- x.y.z.Outer.Inner.VALUE1

As a result, it has unnecessary additional import directives.
This commit fixes the issue by avoiding duplicated shortening for a
single PSI element.

analysis/analysis-api/testData/components/referenceShortener/referenceShortener/classScopes2.txt

@@ -1,11 +1,8 @@
 Before shortening: Child.Foo.check()
 with DO_NOT_SHORTEN:
 with SHORTEN_IF_ALREADY_IMPORTED:
-[qualifier] Child.Foo
 [qualifier] Child.Foo.check()
 with SHORTEN_AND_IMPORT:
-[qualifier] Child.Foo
 [qualifier] Child.Foo.check()
 with SHORTEN_AND_STAR_IMPORT:
-[qualifier] Child.Foo
 [qualifier] Child.Foo.check()

analysis/analysis-api/testData/components/referenceShortener/referenceShortener/enumClassCompanionAlreadyImported.txt

@@ -1,11 +1,8 @@
 Before shortening: a.b.c.MyEnum.Companion.foo()
 with DO_NOT_SHORTEN:
 with SHORTEN_IF_ALREADY_IMPORTED:
-[qualifier] a.b.c.MyEnum
 [qualifier] a.b.c.MyEnum.Companion.foo()
 with SHORTEN_AND_IMPORT:
-[qualifier] a.b.c.MyEnum.Companion
 [qualifier] a.b.c.MyEnum.Companion.foo()
 with SHORTEN_AND_STAR_IMPORT:
-[qualifier] a.b.c.MyEnum.Companion
 [qualifier] a.b.c.MyEnum.Companion.foo()

analysis/analysis-api/testData/components/referenceShortener/referenceShortener/multipleImport.kt

@@ -0,0 +1,16 @@
+// FILE: main.kt
+package a.b.c
+
+fun test(n: Int) {
+    return if (<expr>x.y.z.Outer.Inner.VALUE0 > x.y.z.Outer.Inner.VALUE1</expr>) 1
+    else n
+}
+// FILE: values.kt
+package x.y.z
+
+class Outer {
+    object Inner {
+        val VALUE0 = 13
+        val VALUE1 = 17
+    }
+}

analysis/analysis-api/testData/components/referenceShortener/referenceShortener/multipleImport.txt

@@ -0,0 +1,9 @@
+Before shortening: x.y.z.Outer.Inner.VALUE0 > x.y.z.Outer.Inner.VALUE1
+with DO_NOT_SHORTEN:
+with SHORTEN_IF_ALREADY_IMPORTED:
+with SHORTEN_AND_IMPORT:
+[qualifier] x.y.z.Outer.Inner.VALUE0
+[qualifier] x.y.z.Outer.Inner.VALUE1
+with SHORTEN_AND_STAR_IMPORT:
+[qualifier] x.y.z.Outer.Inner.VALUE0
+[qualifier] x.y.z.Outer.Inner.VALUE1

analysis/analysis-api/testData/components/referenceShortener/referenceShortener/shortenAlreadyImportedFunction2.txt

@@ -1,11 +1,8 @@
 Before shortening: Outer.Inner.foo()
 with DO_NOT_SHORTEN:
 with SHORTEN_IF_ALREADY_IMPORTED:
-[qualifier] Outer.Inner
 [qualifier] Outer.Inner.foo()
 with SHORTEN_AND_IMPORT:
-[qualifier] Outer.Inner
 [qualifier] Outer.Inner.foo()
 with SHORTEN_AND_STAR_IMPORT:
-[qualifier] Outer.Inner
 [qualifier] Outer.Inner.foo()