HS: as Date/Set/Map return real JS host objects (+4 tests)

- hs-coerce "Date": new case returns (host-new "Date" value)
- hs-coerce "Set": creates real JS Set via host-new + for-each add (was SX list)
- hs-coerce "Map": creates real JS Map via host-new + for-each set (was SX list)
- hs-make "Set"/"Map": use host-new instead of (list)/(dict)
- hs-add-to!, hs-remove-from!, hs-empty-like, hs-append: handle real JS Sets
- hs-run-filtered.js: add hs-is-set? and hs-is-map? natives
- generator: MANUAL_TEST_BODIES for converts-as-Date (×2), as-Set, as-Map
asExpression suite: 36/42 (was 32/42)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/playwright/generate-sx-tests.py

@@ -326,6 +326,26 @@ MANUAL_TEST_BODIES = {
         '          (list (list (quote record) record)))',
         '        "<div age=\\"21\\" style=\\"color:bleaux\\">John Connor</div>"))',
     ],
+    # asExpression: Date/Set/Map need real JS host objects
+    "converts value as Date": [
+        '    (let ((_result (eval-hs "1 as Date")))',
+        '      (assert= (host-call _result "getTime") 1))',
+    ],
+    "can use the a modifier if you like": [
+        '    (let ((_result (eval-hs "1 as a Date")))',
+        '      (assert= (host-call _result "getTime") 1))',
+    ],
+    "converts array as Set": [
+        '    (let ((_result (eval-hs "[1,2,2,3] as Set")))',
+        '      (assert (hs-is-set? _result))',
+        '      (assert= (host-get _result "size") 3))',
+    ],
+    "converts object as Map": [
+        '    (let ((_result (eval-hs "{a:1, b:2} as Map")))',
+        '      (assert (hs-is-map? _result))',
+        '      (assert= (host-call _result "get" "a") 1)',
+        '      (assert= (host-get _result "size") 2))',
+    ],
 }