Allow multiple 'this' property assignments in Salsa

Fixes issue #6645

Author: RyanCavanaugh

src/compiler/binder.ts

@@ -1435,7 +1435,8 @@ namespace ts {
             // Declare a 'member' in case it turns out the container was an ES5 class
             if (container.kind === SyntaxKind.FunctionExpression || container.kind === SyntaxKind.FunctionDeclaration) {
                 container.symbol.members = container.symbol.members || {};
-                declareSymbol(container.symbol.members, container.symbol, node, SymbolFlags.Property, SymbolFlags.PropertyExcludes);
+                // It's acceptable for multiple 'this' assignments of the same identifier to occur
+                declareSymbol(container.symbol.members, container.symbol, node, SymbolFlags.Property, SymbolFlags.PropertyExcludes & ~SymbolFlags.Property);
             }
         }
 

tests/cases/fourslash/getJavaScriptSemanticDiagnostics23.ts

@@ -0,0 +1,14 @@
+/// <reference path="fourslash.ts" />
+
+// @allowJs: true
+// @Filename: a.js
+//// function Person(age) {
+////     if (age >= 18) {
+////         this.canVote = true;
+////     } else {
+////         this.canVote = false;
+////     }
+//// }
+
+verify.getSyntacticDiagnostics(`[]`);
+verify.getSemanticDiagnostics(`[]`);