Fix handling of file: module URIs with non-ASCII characters (#696)

Addresses an issue where Pkl cannot evaluate files with non-ASCII characters.

pkl-core/src/test/files/LanguageSnippetTests/input/modules/日本語.pkl

@@ -0,0 +1,6 @@
+// covers https://github.com/apple/pkl/issues/653
+日本語 = "Japanese language"
+readOne = read("日本語.pkl").text
+readGlob = read*("./日*.pkl").keys
+importOne = import("日本語.pkl").readOne
+importGlob = import*("./日*.pkl").keys

pkl-core/src/test/files/LanguageSnippetTests/input/modules/日本語_error.pkl

@@ -0,0 +1,2 @@
+// covers https://github.com/apple/pkl/issues/653
+日本語 = throw("Error reporting should also handle unicode filenames!")

pkl-core/src/test/files/LanguageSnippetTests/output/modules/日本語.pcf

@@ -0,0 +1,21 @@
+日本語 = "Japanese language"
+readOne = """
+  // covers https://github.com/apple/pkl/issues/653
+  日本語 = "Japanese language"
+  readOne = read("日本語.pkl").text
+  readGlob = read*("./日*.pkl").keys
+  importOne = import("日本語.pkl").readOne
+  importGlob = import*("./日*.pkl").keys
+  
+  """
+readGlob = Set("./日本語.pkl", "./日本語_error.pkl")
+importOne = """
+  // covers https://github.com/apple/pkl/issues/653
+  日本語 = "Japanese language"
+  readOne = read("日本語.pkl").text
+  readGlob = read*("./日*.pkl").keys
+  importOne = import("日本語.pkl").readOne
+  importGlob = import*("./日*.pkl").keys
+  
+  """
+importGlob = Set("./日本語.pkl", "./日本語_error.pkl")

pkl-core/src/test/files/LanguageSnippetTests/output/modules/日本語_error.err

@@ -0,0 +1,10 @@
+–– Pkl Error ––
+Error reporting should also handle unicode filenames!
+
+x | 日本語 = throw("Error reporting should also handle unicode filenames!")
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at 日本語_error#日本語 (file:///$snippetsDir/input/modules/%E6%97%A5%E6%9C%AC%E8%AA%9E_error.pkl)
+
+xxx | text = renderer.renderDocument(value)
+             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+at pkl.base#Module.output.text (pkl:base)