With nested jars there are two different mechanisms that will be
used as the path is not usable as a `java.nio.file.Path` instance.

The first is trying to convert the resulting nested path - a path
like `jar:file:....!/some/nested/path` - to a `URL` and if that should
fail due to a `MalformedURLException` it is tried to convert
the path to `URI`. If the URI fallback fails an IOException will
be thrown and this eventually will bubble up and discard the whole
classpath entry, resulting in a message like the following when
enabling verbose output during scanning:

```
2023-11-02T12:51:42.719+0100	ClassGraph	-- Skipping invalid classpath entry .../spring-boot-fully-executable-jar.jar!/BOOT-INF/lib/... : java.io.IOException: Malformed URI: ...
```

Most of the time nothing will be discarded as most paths can be converted
to a URL in the first step or at least succeed when converting to a URI.

However for paths containing spaces and the hash symbol we can reach a
case where both URL conversion and URI conversion fail and so the
classpath entry is discarded even though all paths are valid and can
be usable.

Let us assume a Spring Boot Executable JAR that is located in a directory
named `ci-build main classgraph#123` - which is a valid directory name on Windows
and Linux.

When ClassGraph reaches a nested library here it will construct the
paths to the nested jars like `jar:file:<path>!/<nested-path>`.

So in this case we end up with something like `jar:file:/opt/ci-build main classgraph#123!/BOOT-INF/lib/my-lib.jar`.

When ClassGraph reaches the conversion code it will first try to convert
to a URL. This will fail with the following message:

`java.net.MalformedURLException: no !/ in spec`

If we then fallback to the URI conversion it will try to convert but as
our path contains spaces this will also be rejected by an exception:

`java.net.URISyntaxException: Illegal character in opaque part at index 66: jar:file:...`

The index will point to the first space in the path that is converted.

So we can construct nested paths that are neither valid `URL` instances
nor valid `URI instances`.

To solve this issue we introduce encoding for spaces when the path
is handled as a url or multi-section path to ensure that conversion
can succeed. This seems to also be what the `java.nio.file.Path` API
does when asking for the resulting URI for the same path.

So this commit encodes spaces as `%20` and hash symbols as `%23` when
going into the URL/Multi-Section branch.

Fixes classgraph#804