DLS: Be better at matching an open file URI to a compiler instance

The DLS runs as many compiler instances as there are subprojects in the
build . When a file is opened we need to decide which compiler instance
should handle it, this is done by matching the file URI against the
source directories configured for each subproject. This commit improves
this matching in two way:
- Use URI#getPath instead of URI#getRawPath to decode percent-encoded
characters in the URI
- Use File#getCanonicalPath instead of File#getAbsolutePath

The first fix is necessary to get the DLS running in Windows, because
URIs start with file:///C%3A/.../ and we need getPath to decode "C%3A" to "C:".

Author: smarter

language-server/src/dotty/tools/languageserver/DottyLanguageServer.scala

@@ -76,7 +76,7 @@ class DottyLanguageServer extends LanguageServer
   def driverFor(uri: URI): InteractiveDriver = {
     val matchingConfig =
       drivers.keys.find(config => config.sourceDirectories.exists(sourceDir =>
-        uri.getRawPath.startsWith(sourceDir.getAbsolutePath.toString)))
+        new File(uri.getPath).getCanonicalPath.startsWith(sourceDir.getCanonicalPath)))
     matchingConfig match {
       case Some(config) =>
         drivers(config)