Improve error message for invalid input

[remkop]

Related to checkstyle/checkstyle#6082 :

Currently the error message for invalid input is not very user-friendly.

For example, if a non-numeric value is specified for an option of type int:

Could not convert 'invalid' to int for option '--tree-walker-threads-number': java.lang.NumberFormatException: For input string: "invalid"

Another example: if an invalid value if specified for an enum:

Could not convert 'xmlp' to OutputFormat for option '-f': java.lang.IllegalArgumentException: No enum constant com.puppycrawl.tools.checkstyle.Main.OutputFormat.xmlp

Instead:

• Invalid value for option '--tree-walker-threads-number': 'invalid' could not be converted to 'int'. (java.lang.NumberFormatException: For input string: "invalid")
• Invalid value 'xmlp' for option '-f': valid values are [xml, plain].