Rearrange stdlib unit tests across packages.

Rearrange JS stdlib unit tests.

libraries/stdlib/test/numbers/MathJVMTest.kt

@@ -0,0 +1,39 @@
+package test.numbers
+
+import java.math.BigInteger
+import java.math.BigDecimal
+
+import kotlin.test.*
+import org.junit.Test as test
+
+class MathTest {
+    @test fun testBigInteger() {
+        val a = BigInteger("2")
+        val b = BigInteger("3")
+
+        assertEquals(BigInteger("5"), a + b)
+        assertEquals(BigInteger("-1"), a - b)
+        assertEquals(BigInteger("6"), a * b)
+        assertEquals(BigInteger("0"), a / b)
+        assertEquals(BigInteger("-2"), -a)
+        assertEquals(BigInteger("1"), -a % b)
+        assertEquals(BigInteger("-2"), (-a).remainder(b))
+    }
+
+    @test fun testBigDecimal() {
+        val a = BigDecimal("2")
+        val b = BigDecimal("3")
+
+        assertEquals(BigDecimal("5"), a + b)
+        assertEquals(BigDecimal("-1"), a - b)
+        assertEquals(BigDecimal("6"), a * b)
+        assertEquals(BigDecimal("2"), BigDecimal("4") / a)
+        assertEquals(BigDecimal("-2"), -a)
+        assertEquals(BigDecimal("-2"), -a % b)
+    }
+}
+
+fun main(args: Array<String>) {
+    MathTest().testBigInteger()
+    MathTest().testBigDecimal()
+}