Merge bitcoin/bitcoin#24675: util: Use ArgsManager::GetPathArg more widely

b01f336708 util, refactor: Drop explicit conversion to fs::path (Hennadii Stepanov)
138c668e2b util, refactor: Use GetPathArg to read "-rpccookiefile" value (Hennadii Stepanov)
1276090705 util, refactor: Use GetPathArg to read "-conf" value (Hennadii Stepanov)

Pull request description:

  This PR is a continuation of bitcoin/bitcoin#24265 and bitcoin/bitcoin#24306.

  Now the following command-line arguments / configure options been read with the `GetPathArg` method:
  - `-conf`, also `includeconf` values been normalized
  - `-rpccookiefile`

ACKs for top commit:
  jarolrod:
    Code Review ACK b01f336708
  ryanofsky:
    Code review ACK b01f336708. Changes since last review: just dropping first commit (NormalizedPathFromString) as suggested

Tree-SHA512: 2d26d50b73542acdbcc63a32068977b2a49a017d31ca337471a0446f964eb0a6e3e4e3bb1ebe6771566a260f2cae3bc2ebe93b4b523183cea0d51768daab85c9

src/qt/guiutil.cpp

@@ -428,7 +428,7 @@ void openDebugLogfile()
 
 bool openBitcoinConf()
 {
-    fs::path pathConfig = GetConfigFile(gArgs.GetArg("-conf", BITCOIN_CONF_FILENAME));
+    fs::path pathConfig = GetConfigFile(gArgs.GetPathArg("-conf", BITCOIN_CONF_FILENAME));
 
     /* Create the file */
     std::ofstream configFile{pathConfig, std::ios_base::app};