refactor(firestore): remove variable expression handling from multiple platforms

Author: SelaseKay

packages/cloud_firestore/cloud_firestore/android/src/main/java/io/flutter/plugins/firebase/firestore/utils/ExpressionParsers.java

@@ -136,14 +136,6 @@ Expression parseExpression(@NonNull Map<String, Object> expressionMap) {
           }
           return Expression.field(fieldName);
         }
-      case "variable":
-        {
-          String variableName = (String) args.get("name");
-          if (variableName == null) {
-            throw new IllegalArgumentException("Variable expression must have a 'name' argument");
-          }
-          return Expression.variable(variableName);
-        }
       case "constant":
         {
           Object value = args.get("value");

packages/cloud_firestore/cloud_firestore/ios/cloud_firestore/Sources/cloud_firestore/FLTPipelineParser.m

@@ -116,16 +116,6 @@ - (FIRExprBridge *)parseExpression:(NSDictionary<NSString *, id> *)map error:(NS
     return [[FIRFieldBridge alloc] initWithName:field];
   }
 
-  if ([name isEqualToString:@"variable"]) {
-    NSString *variableName = args[@"name"];
-    if (![variableName isKindOfClass:[NSString class]] || variableName.length == 0) {
-      if (error) *error = parseError(@"Variable expression requires 'name' argument");
-      return nil;
-    }
-    return FLTNewFunctionExprBridge(@"variable",
-                                    @[ [[FIRConstantBridge alloc] init:variableName] ]);
-  }
-
   if ([name isEqualToString:@"constant"]) {
     id value = args[@"value"];
     if (value == nil) {

packages/cloud_firestore/cloud_firestore/pipeline_example/integration_test/pipeline/pipeline_expressions_e2e.dart

@@ -820,28 +820,23 @@ void runPipelineExpressionsTests() {
       expect(snapshot.result[0].data()!['tags_rev'], ['q', 'p']);
     });
 
-    test(
-      'addFields with arraySlice returns sliced array',
-      () async {
-        final snapshot = await firestore
-            .pipeline()
-            .collection('pipeline-e2e')
-            .where(Expression.field('test').equalValue('expressions'))
-            .where(Expression.field('score').equalValue(50))
-            .addFields(
-              Expression.field('arr').arraySlice(1, 2).as('arr_slice'),
-            )
-            .limit(1)
-            .execute();
+    test('addFields with arraySlice returns sliced array', () async {
+      final snapshot = await firestore
+          .pipeline()
+          .collection('pipeline-e2e')
+          .where(Expression.field('test').equalValue('expressions'))
+          .where(Expression.field('score').equalValue(50))
+          .addFields(Expression.field('arr').arraySlice(1, 2).as('arr_slice'))
+          .limit(1)
+          .execute();
 
-        expectResultCount(snapshot, 1);
-        expectResultsData(snapshot, [
-          {
-            'arr_slice': [4, 6],
-          },
-        ]);
-      },
-    );
+      expectResultCount(snapshot, 1);
+      expectResultsData(snapshot, [
+        {
+          'arr_slice': [4, 6],
+        },
+      ]);
+    });
 
     test(
       'arraySum addFields succeeds on Android',

packages/cloud_firestore/cloud_firestore_web/lib/src/interop/firestore_interop.dart

@@ -353,7 +353,6 @@ extension type PipelinesJsImpl._(JSObject _) implements JSObject {
 
   // --- Expression builders ---
   external ExpressionJsImpl field(JSString path);
-  external ExpressionJsImpl variable(JSString name);
   external ExpressionJsImpl constant(JSAny? value);
 
   // --- Boolean / comparison ---

packages/cloud_firestore/cloud_firestore_web/lib/src/pipeline_expression_parser_web.dart

@@ -40,8 +40,6 @@ class PipelineExpressionParserWeb {
     switch (name) {
       case 'field':
         return _pipelines.field(((argsMap[_kField] as String?) ?? '').toJS);
-      case 'variable':
-        return _pipelines.variable(((argsMap[_kName] as String?) ?? '').toJS);
       case 'add':
         return _binaryArithmetic(argsMap, (l, r) => l.add(r));
       case 'subtract':