Rename CFE Severity enum.

The analyzer already has an enum with the same name, but a slightly
different declaration. (The analyzer's enum declares only severities
of `error`, `warning`, and `info`, whereas the CFE's enum also
declares severities of `context`, `ignored`, and `internalProblem`).

I'm currently embarking on an arc of work that I hope will eventually
culminate in unifying the analyzer and CFE diagnostic message
representations (and their severities) into a single set of
classes. Until that unification is complete, both representations will
have to co-exist in the `_fe_analyzer_shared` package. To reduce
confusion during that time period, I would like the classes to have
distinct names.

Since the analyzer's `Severity` enum is exposed through the analyzer
public API, analyzer clients may depend on the name. So it makes sense
to rename the CFE's `Severity` enum.

Tested: standard trybots
Change-Id: I95622950f49b1754267e441e4636e046045629bb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/442102
Reviewed-by: Liam Appelbe <[email protected]>
Reviewed-by: Mayank Patke <[email protected]>
Commit-Queue: Paul Berry <[email protected]>
Reviewed-by: Ömer Ağacan <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: stereotype441

pkg/_fe_analyzer_shared/lib/src/messages/codes.dart

@@ -10,7 +10,7 @@ import 'diagnostic_message.dart' show CfeDiagnosticMessage;
 
 import '../scanner/token.dart' show Token;
 
-import 'severity.dart' show Severity;
+import 'severity.dart' show CfeSeverity;
 
 import '../util/relativize.dart' as util show isWindows, relativizeUri;
 
@@ -28,13 +28,13 @@ class Code {
 
   final List<String>? analyzerCodes;
 
-  final Severity severity;
+  final CfeSeverity severity;
 
   const Code(
     this.name, {
     this.index = -1,
     this.analyzerCodes,
-    this.severity = Severity.error,
+    this.severity = CfeSeverity.error,
   });
 
   @override
@@ -161,7 +161,7 @@ class LocatedMessage implements Comparable<LocatedMessage> {
     PlainAndColorizedString formatted,
     int line,
     int column,
-    Severity severity,
+    CfeSeverity severity,
     List<FormattedMessage>? relatedInformation, {
     List<Uri>? involvedFiles,
   }) {
@@ -227,7 +227,7 @@ class FormattedMessage implements CfeDiagnosticMessage {
   final int column;
 
   @override
-  final Severity severity;
+  final CfeSeverity severity;
 
   final List<FormattedMessage>? relatedInformation;
 
@@ -308,7 +308,7 @@ class DiagnosticMessageFromJson implements CfeDiagnosticMessage {
   final Iterable<String> plainTextFormatted;
 
   @override
-  final Severity severity;
+  final CfeSeverity severity;
 
   final Uri? uri;
 
@@ -335,7 +335,7 @@ class DiagnosticMessageFromJson implements CfeDiagnosticMessage {
     List<String> plainTextFormatted = _asListOfString(
       decoded["plainTextFormatted"],
     );
-    Severity severity = Severity.values[decoded["severity"] as int];
+    CfeSeverity severity = CfeSeverity.values[decoded["severity"] as int];
     Uri? uri =
         decoded["uri"] == null ? null : Uri.parse(decoded["uri"] as String);
     List<Uri>? involvedFiles =