bazel syntax: rename ParserInput{Source,}

Also:
- make it concrete and final
- hide the getContent method, to allow the possibility of a scanner
  using code points or UTF-8 bytes, not UTF-16 chars.

This is necessarily a breaking API change for copybara.

RELNOTES: N/A
PiperOrigin-RevId: 269623736
diff --git a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
index ee94110..1a4b40a 100644
--- a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkRuleClassFunctionsTest.java
@@ -53,7 +53,7 @@
 import com.google.devtools.build.lib.syntax.Environment;
 import com.google.devtools.build.lib.syntax.EvalException;
 import com.google.devtools.build.lib.syntax.EvalUtils;
-import com.google.devtools.build.lib.syntax.ParserInputSource;
+import com.google.devtools.build.lib.syntax.ParserInput;
 import com.google.devtools.build.lib.syntax.SkylarkDict;
 import com.google.devtools.build.lib.syntax.SkylarkList.MutableList;
 import com.google.devtools.build.lib.syntax.SkylarkList.Tuple;
@@ -703,7 +703,7 @@
   }
 
   protected void evalAndExport(String... lines) throws Exception {
-    ParserInputSource input = ParserInputSource.fromLines(lines);
+    ParserInput input = ParserInput.fromLines(lines);
     BuildFileAST file = BuildFileAST.parseAndValidateSkylark(input, ev.getEnvironment());
     SkylarkImportLookupFunction.execAndExport(
         file, FAKE_LABEL, ev.getEventHandler(), ev.getEnvironment());