test: validate missing encoding in to_string

[anonrig]

Validates cloudflare/workerd#1777 bug.

[anonrig]

We might have a bug with character sets.

• The application/x-www-form-urlencoded percent-encode set is the component percent-encode set and U+0021 (!), U+0027 (') to U+0029 RIGHT PARENTHESIS, inclusive, and U+007E (~).
• The component percent-encode set is the userinfo percent-encode set and U+0024 ($) to U+0026 (&), inclusive, U+002B (+), and U+002C (,).
• The userinfo percent-encode set is the path percent-encode set and U+002F (/), U+003A (:), U+003B (;), U+003D (=), U+0040 (@), U+005B ([) to U+005E (^), inclusive, and U+007C (|).

The user info percent-encode set contains /, but it doesn't get encoded.

cc @lemire

[lemire]

@anonrig Nice fix. :-)

I like that you added a test.