$(a: float) now works consistently in nim js, avoiding printing floats as ints (#14134)

* fix https://github.com/timotheecour/Nim/issues/133; $(a: float) works in nim js like in other backends

* fix tests

* fix test for windows that prints 1.1e17 differently than other OS

tests/js/tdollar_float.nim

@@ -0,0 +1,62 @@
+#[
+merge into tests/system/tdollars.nim once https://github.com/nim-lang/Nim/pull/14122
+is merged
+]#
+
+import unittest
+
+block: # https://github.com/timotheecour/Nim/issues/133
+  # simple test
+  var a: float = 2
+  check $a == "2.0"
+
+  # systematic tests
+  template fun(a2: static float) =
+    const a: float = a2 # needed pending https://github.com/timotheecour/Nim/issues/132
+    var b = a
+    check $b == $a
+
+  fun 2
+  fun 2.0
+  fun 2.1
+  fun 1_000
+  fun 1_000.1
+  fun 1_000_000_000.1
+  fun 1_000_000_000_000.1
+
+  # negatives
+  fun -2.0
+  fun -2.1
+
+  # 0
+  fun 0
+  fun -0
+  fun 0.0
+
+  block:
+    var a = -0.0
+    check $a in ["-0.0", "0.0"]
+
+  # exponents
+  block:
+    var a = 5e20
+    check $a in ["5e20", "500000000000000000000.0"]
+
+  fun 3.4e1'f32
+  fun 3.4e-1'f32
+  fun -3.4e-1'f32
+  fun 3.4e-1'f32
+  fun 3e-1'f32
+
+  block:
+    var a = 3.4e38'f32
+    check $a in ["3.4e+38", "3.4e+038"]
+      # on windows, printf (used in VM) prints as 3.4e+038
+      # but js prints as 3.4e+38
+      # on osx, both print as 3.4e+38
+      # see https://github.com/timotheecour/Nim/issues/138
+
+  when false: # edge cases
+    fun -0.0 # see https://github.com/timotheecour/Nim/issues/136
+    fun 5e20
+    fun 3.4e38'f32