Generate docs for floorDiv and mod and improve docs for div and rem

Refactor operator documentation generation for primitives and unsigned
types so that it is easier to specialize it.

Manually sync docs of numeric types in js-ir stdlib.

 KT-26234

generators/builtins/common.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.generators.builtins
 
 import org.jetbrains.kotlin.generators.builtins.ProgressionKind.*
+import java.io.PrintWriter
 
 enum class PrimitiveType(val byteSize: Int) {
     BYTE(1),
@@ -65,3 +66,15 @@ fun hashLong(v: String) = "($v xor ($v ushr 32))"
 fun convert(v: String, from: UnsignedType, to: UnsignedType) = if (from == to) v else "$v.to${to.capitalized}()"
 
 fun convert(v: String, from: PrimitiveType, to: PrimitiveType) = if (from == to) v else "$v.to${to.capitalized}()"
+
+
+fun PrintWriter.printDoc(documentation: String, indent: String) {
+    val docLines = documentation.lines()
+    if (docLines.size == 1) {
+        this.println("$indent/** $documentation */")
+    } else {
+        this.println("$indent/**")
+        docLines.forEach { this.println("$indent * $it") }
+        this.println("$indent */")
+    }
+}