Implement URI for pure Wasm (scala-wasm#151)

Add linkTimeIf branches for all JS-dependent operations in URI:
- URI parsing: js.RegExp.exec() → java.util.regex.Pattern
- Path normalization: js.Array + .join() → Scala Array + StringBuilder
- IPv6 detection: js.RegExp.test() → java.util.regex.Pattern
- Quoting (5 functions): jsReplace(regex, callback) → quoteWithPattern()
- UTF-8 percent-encoding: pure Scala via StandardCharsets.UTF_8

Remove top-level vals with JS types (RegExp, js.Function1) to avoid
linker errors; inline them into linkTimeIf JS branches instead.

Unblock URITest in pure Wasm test suite. Add 6 new tests covering
multi-component quoting, IPv6, normalize edge cases, and non-ASCII.

Author: v.karamyshev