Normalize asset paths in local dependencies (#1737)

This changes local asset path resolution so that `..` segments at the
dependency root just resolves to the dependency root.

This makes import resolution work the same between local and remote dependencies.

pkl-core/src/test/files/LanguageSnippetTests/input/projects/project1/localProject2.pkl

@@ -0,0 +1,3 @@
+// `..` at the package root stays in the package root
+res1 = import("@project2/../penguin.pkl")
+res2 = import("@project2/foo/../../penguin.pkl")

pkl-core/src/test/files/LanguageSnippetTests/input/projects/project1/localProjectRead2.pkl

@@ -0,0 +1,3 @@
+res1 = read*("@project2/../*").keys
+res2 = read*("@project2/../../*").keys
+res3 = read("@project2/../../").text

pkl-core/src/test/files/LanguageSnippetTests/output/projects/project1/localProject2.pcf

@@ -0,0 +1,16 @@
+res1 {
+  bird {
+    name = "Penguin"
+    favoriteFruit {
+      name = "Ice Fruit"
+    }
+  }
+}
+res2 {
+  bird {
+    name = "Penguin"
+    favoriteFruit {
+      name = "Ice Fruit"
+    }
+  }
+}

pkl-core/src/test/files/LanguageSnippetTests/output/projects/project1/localProjectRead2.pcf

@@ -0,0 +1,8 @@
+res1 = Set("@project2/../PklProject", "@project2/../PklProject.deps.json", "@project2/../penguin.pkl")
+res2 = Set("@project2/../../PklProject", "@project2/../../PklProject.deps.json", "@project2/../../penguin.pkl")
+res3 = """
+  penguin.pkl
+  PklProject
+  PklProject.deps.json
+  
+  """