Migrate from deprecated URLEncoder to URI

[marevol]

java.net.URL has been deprecated in recent Java versions, so this commit migrates all usages to the recommended java.net.URI class.

Changes:

• ProtocolHelper.java: Convert URL to URI using toURI() method for ClassLoader resources, update protocol checks to use getScheme() instead of getProtocol()
• FessXpathTransformer.java: Replace all URL instances with URI, use URI.create() and URI.resolve() for URL construction and relative URL resolution, update exception handling from MalformedURLException to IllegalArgumentException

Note: fess-crawler library changes are handled separately as mentioned by the user.