Fix stale string definitions during hot-swapping

IDE/Tests/Test1/scripts/HotSwap_StringLiterals.txt

@@ -0,0 +1,20 @@
+ShowFile("src/HotSwap_StringLiterals.bf")
+
+# Build with the literal, then remove its usage and rebuild without cleaning.
+ToggleCommentAt("UseString")
+Compile()
+AssertCompileSucceeded()
+ToggleCommentAt("UseString")
+Compile()
+AssertCompileSucceeded()
+
+GotoText("//StringPool_Start")
+ToggleBreakpoint()
+RunWithCompiling()
+AssertEvalEquals("GetLength()", "0")
+
+# The hot update must emit the literal omitted from the executable being debugged.
+ToggleCommentAt("UseString")
+Compile()
+AssertCompileSucceeded()
+AssertEvalEquals("GetLength()", "15")

IDE/Tests/Test1/src/HotSwap_StringLiterals.bf

@@ -0,0 +1,30 @@
+using System;
+
+#pragma warning disable 168
+
+namespace IDETest
+{
+	class HotSwap_StringLiterals
+	{
+		// A separate module lets the literal become unused when its call is removed.
+		class StringSource
+		{
+			public static String GetValue() => "hot-swap string";
+		}
+
+		static int GetLength()
+		{
+			int length = 0;
+			/*UseString
+			length = StringSource.GetValue().Length;
+			*/
+			return length;
+		}
+
+		public static void Test()
+		{
+			//StringPool_Start
+			int length = GetLength();
+		}
+	}
+}

IDE/Tests/Test1/src/Program.bf

@@ -21,6 +21,7 @@ namespace IDETest
 			HotSwap_LiveTypes.Test();
 			HotSwap_LocateSym01.Test();
 			HotSwap_Reflection.Test();
+			HotSwap_StringLiterals.Test();
 			HotSwap_TLS.Test();
 			InlineTester.Test();
 			LambdaTester.Test();

IDEHelper/Compiler/BfCompiler.cpp

@@ -1453,6 +1453,8 @@ void BfCompiler::CreateVData(BfVDataModule* bfModule)
 		CompileLog("VData unchanged, skipping\n");
 		return;
 	}
+	if (!isHotCompile)
+		bfModule->mDefinedStrings.Clear();
 
 	auto typeResolveModule = mContext->mUnreifiedModule;
 	BfTypeInstance* stringType = typeResolveModule->ResolveTypeDef(mStringTypeDef, BfPopulateType_Data)->ToTypeInstance();