[HTTP] Create a dedicated file table entry for each HttpRequest::getContentDescriptor()

(HttpRequest): Refine
(HttpRequest::getFilePath, HttpRequest::removeFile, HttpCache::getFilePath): New
(HttpCache::notify, HttpCache::invalidate, HttpCache::~HttpCache): Refine
(HttpCacheManager::send, HttpCacheManager::~HttpCacheManager): Refine
(HttpCacheManager::dump): New
(Parser::Parser, CSSImportRuleImp::notify, HTMLLinkElementImp::linkStyleSheet, HTMLScriptElementImp::execute): Refine