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)

tests/stdlib/tjson.nim

@@ -314,8 +314,7 @@ block: # bug #17383
   else:
     testRoundtrip(int.high): "9223372036854775807"
     testRoundtrip(uint.high): "18446744073709551615"
-  whenJsNoBigInt64: discard
-  do:
+  when hasWorkingInt64:
     testRoundtrip(int64.high): "9223372036854775807"
     testRoundtrip(uint64.high): "18446744073709551615"
 

tests/stdlib/trandom.nim

@@ -225,8 +225,9 @@ block: # same as above but use slice overload
       doAssert a3.type is a2.type
   test cast[uint](int.high)
   test cast[uint](int.high) + 1
-  whenJsNoBigInt64: discard
-  do:
+  when hasWorkingInt64 and defined(js):
+    # weirdly this has to run only in JS for the final int32.high test
+    # to be the same between C/C++ and --jsbigint64:on
     test uint64.high
     test uint64.high - 1
   test uint.high - 2

tests/stdlib/tstrutils.nim

@@ -527,8 +527,7 @@ template main() =
 
   block: # toHex
     doAssert(toHex(100i16, 32) == "00000000000000000000000000000064")
-    whenJsNoBigInt64: discard
-    do:
+    when hasWorkingInt64:
       doAssert(toHex(-100i16, 32) == "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFF9C")
       doAssert(toHex(high(uint64)) == "FFFFFFFFFFFFFFFF")
       doAssert(toHex(high(uint64), 16) == "FFFFFFFFFFFFFFFF")
@@ -550,9 +549,8 @@ template main() =
     doAssert(spaces(0) == "")
 
   block: # toBin, toOct
-    whenJsNoBigInt64: # bug #11369
-      discard
-    do:
+    when hasWorkingInt64:
+      # bug #11369
       var num: int64 = -1
       doAssert num.toBin(64) == "1111111111111111111111111111111111111111111111111111111111111111"
       doAssert num.toOct(24) == "001777777777777777777777"
@@ -773,8 +771,7 @@ bar
 
   block: # formatSize
     disableVm:
-      whenJsNoBigInt64: discard
-      do:
+      when hasWorkingInt64:
         doAssert formatSize((1'i64 shl 31) + (300'i64 shl 20)) == "2.293GiB" # <=== bug #8231
       doAssert formatSize((2.234*1024*1024).int) == "2.234MiB"
       doAssert formatSize(4096) == "4KiB"