isAbsolute method
Returns true if path is an absolute path and false if it is a
relative path.
On POSIX systems, absolute paths start with a / (forward slash). On
Windows, an absolute path starts with \\, or a drive letter followed by
:/ or :\. For URLs, absolute paths either start with a protocol and
optional hostname (e.g. https://dart.dev, file://) or with a /.
URLs that start with / are known as "root-relative", since they're
relative to the root of the current URL. Since root-relative paths are still
absolute in every other sense, isAbsolute will return true for them. They
can be detected using isRootRelative.
Implementation
bool isAbsolute(String path) => p.context.isAbsolute(path);