improve compression of undefined, NaN & Infinitiy (#1748)

- migrate transformation logic from `OutputStream` to `Compressor`
- always turn `undefined` into `void 0` (unless `unsafe`)
- always keep `NaN` except when avoiding local variable redefinition
- introduce `keep_infinity` to suppress `1/0` transform, except when avoiding local variable redefinition

supersedes #1723
fixes #1730

test/compress/evaluate.js

@@ -52,7 +52,7 @@ and: {
         a = 7;
 
         a = false;
-        a = 0/0;
+        a = NaN;
         a = 0;
         a = void 0;
         a = null;
@@ -67,7 +67,7 @@ and: {
         a = 6 << condition   && -4.5;
 
         a = condition        && false;
-        a = console.log("b") && 0/0;
+        a = console.log("b") && NaN;
         a = console.log("c") && 0;
         a = 2 * condition    && void 0;
         a = condition + 3    && null;
@@ -149,7 +149,7 @@ or: {
         a = 6 << condition   || -4.5;
 
         a = condition        || false;
-        a = console.log("b") || 0/0;
+        a = console.log("b") || NaN;
         a = console.log("c") || 0;
         a = 2 * condition    || void 0;
         a = condition + 3    || null;
@@ -533,7 +533,7 @@ unsafe_array: {
             [1, 2, 3, a][0] + 1,
             2,
             3,
-            0/0,
+            NaN,
             "1,21",
             5,
             (void 0)[1] + 1