Port TypeScript PR #60195: Allow reusing error type annotations

This change allows type node annotations that resolve to error types to be reused in isolated declarations mode. This prevents cascading errors when source code contains unresolved type references.

The fix adds:
1. A check in tryReuseExistingNonParameterTypeNode to detect error types and allow reuse
2. Logic in serializeTypeForDeclaration to attempt reusing existing type annotations before generating new ones

This matches the behavior from microsoft/TypeScript#60195 which fixes issue #60192.

Co-authored-by: RyanCavanaugh <[email protected]>

Author: Copilot

internal/checker/nodebuilderimpl.go

@@ -411,6 +411,13 @@ func (b *nodeBuilderImpl) tryReuseExistingNonParameterTypeNode(existing *ast.Typ
 	if annotationType == nil {
 		annotationType = b.getTypeFromTypeNode(existing, true)
 	}
+	if annotationType != nil && b.ch.isErrorType(annotationType) {
+		// allow "reusing" type nodes that resolve to error types
+		// those can't truly be reused but it prevents cascading errors in isolatedDeclarations
+		// for source with errors there is no guarantee to emit correct code anyway
+		// Since tryReuseExistingTypeNodeHelper is not yet implemented, directly return the existing node
+		return existing
+	}
 	if annotationType != nil && b.typeNodeIsEquivalentToType(host, t, annotationType) && b.existingTypeNodeIsNotReferenceOrIsReferenceWithCompatibleTypeArgumentCount(existing, t) {
 		result := b.tryReuseExistingTypeNodeHelper(existing)
 		if result != nil {
@@ -2006,6 +2013,15 @@ func (b *nodeBuilderImpl) serializeTypeForDeclaration(declaration *ast.Declarati
 		t = b.ch.getOptionalType(t, false)
 	}
 
+	// Try to reuse existing type annotation if present
+	if declaration != nil && declaration.Type() != nil {
+		typeAnnotation := declaration.Type()
+		reused := b.tryReuseExistingTypeNode(typeAnnotation, t, declaration, addUndefinedForParameter)
+		if reused != nil {
+			return reused
+		}
+	}
+
 	restoreFlags := b.saveRestoreFlags()
 	if t.flags&TypeFlagsUniqueESSymbol != 0 && t.symbol == symbol && (b.ctx.enclosingDeclaration == nil || core.Some(symbol.Declarations, func(d *ast.Declaration) bool {
 		return ast.GetSourceFileOfNode(d) == b.ctx.enclosingFile