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.

changelog.md

@@ -96,6 +96,16 @@
 with other backends. see #9125. Use `-d:nimLegacyJsRound` for previous behavior.
 - Added `socketstream` module that wraps sockets in the stream interface
 
+- Changed the behavior of `uri.decodeQuery` when there are unencoded `=`
+  characters in the decoded values. Prior versions would raise an error. This is
+  no longer the case to comply with the HTML spec and other languages
+  implementations. Old behavior can be obtained with
+  `-d:nimLegacyParseQueryStrict`. `cgi.decodeData` which uses the same
+  underlying code is also updated the same way.
+
+
+
+
 - Added `math.signbit`.
 
 - Removed the optional `longestMatch` parameter of the `critbits._WithPrefix` iterators (it never worked reliably)