Merge pull request #19663 from lorentey/default-subscript-is-slow

[stdlib] Force-inline Dictionary.subscript(_:, default:)._modify
diff --git a/stdlib/public/core/Dictionary.swift b/stdlib/public/core/Dictionary.swift
index cc15df4..8169357 100644
--- a/stdlib/public/core/Dictionary.swift
+++ b/stdlib/public/core/Dictionary.swift
@@ -933,6 +933,7 @@
     get {
       return _variant.lookup(key) ?? defaultValue()
     }
+    @inline(__always)
     _modify {
       let (bucket, found) = _variant.mutatingFind(key)
       let native = _variant.asNative