clean up stdlib with --jsbigint64 (#24255)

refs #6978, refs #6752, refs #21613, refs #24234

The `jsNoInt64`, `whenHasBigInt64`, `whenJsNoBigInt64` templates are
replaced with bool constants to use with `when`. Weird that I didn't do
this in the first place.

The `whenJsNoBigInt64` template was also slightly misleading. The first
branch was compiled for both no bigint64 on JS as well as on C/C++. It
seems only `trandom` depended on this by mistake.

The workaround for #6752 added in #6978 to `times` is also removed with
`--jsbigint64:on`, but #24233 was also encountered with this, so this PR
depends on #24234.

(cherry picked from commit 041098e882)

lib/std/private/jsutils.nim

@@ -83,14 +83,21 @@ when defined(js):
         assert 9007199254740991.toJs.isSafeInteger
         assert not 9007199254740992.toJs.isSafeInteger
 
-template whenJsNoBigInt64*(no64, yes64): untyped =
+const jsNoBigInt64* =
   when defined(js):
     when compiles(compileOption("jsbigint64")):
-      when compileOption("jsbigint64"):
-        yes64
-      else:
-        no64
+      not compileOption("jsbigint64")
     else:
-      no64
+      true
   else:
-    no64
+    false
+
+const hasWorkingInt64* =
+  # equal to `not jsNoBigInt64`, but define it by itself anyway
+  when defined(js):
+    when compiles(compileOption("jsbigint64")):
+      compileOption("jsbigint64")
+    else:
+      false
+  else:
+    true