Improve uri.parseQuery to never raise an error (#16647)

In case of malformed query string where there is `=` on the value, handle
this character as part of the value instead of throwing an error.

The following query string should no longer crash a program:

    key=value&key2=x=1

It will be interpreted as [("key", "value"), ("key2", "x=1")]

This is correct according to latest WhatWG's HTML5 specification
recarding the urlencoded parser:
https://url.spec.whatwg.org/#concept-urlencoded-parser

Older behavior can be restored using the -d:nimLegacyParseQueryStrict
flag.

tests/stdlib/turi.nim

@@ -287,8 +287,7 @@ template main() =
 
   block: # decodeQuery
     doAssert toSeq(decodeQuery("a=1&b=0")) == @[("a", "1"), ("b", "0")]
-    doAssertRaises(UriParseError):
-      discard toSeq(decodeQuery("a=1&b=2c=6"))
+    doAssert toSeq(decodeQuery("a=1&b=2c=6")) == @[("a", "1"), ("b", "2c=6")]
 
 static: main()
 main()