fix: change ResolvedConfig type to interface to allow extending it

[lazuee]

Description

This PR changes ResolvedConfig from a type to an interface, allowing it to be extended for various use cases, including plugin development.

Closes: #15473

[hi-ogawa]

Looking at your example #15473 (comment) where optional one is in UserConfig and strict one is in ResolvedConfig, I think this change makes sense.

The build failure is probably because dts bundling is too sensitive to some ordering. Can you try this diff?

Diff

diff --git a/packages/vite/rollup.dts.config.ts b/packages/vite/rollup.dts.config.ts
index 46306f0a2..f1ba14b3b 100644
--- a/packages/vite/rollup.dts.config.ts
+++ b/packages/vite/rollup.dts.config.ts
@@ -50,10 +50,10 @@ const identifierReplacements: Record<string, Record<string, string>> = {
     Plugin$1: 'rollup.Plugin',
     PluginContext$1: 'rollup.PluginContext',
     TransformPluginContext$1: 'rollup.TransformPluginContext',
-    TransformResult$2: 'rollup.TransformResult',
+    TransformResult$1: 'rollup.TransformResult',
   },
   esbuild: {
-    TransformResult$1: 'esbuild_TransformResult',
+    TransformResult$2: 'esbuild_TransformResult',
     TransformOptions$1: 'esbuild_TransformOptions',
     BuildOptions$1: 'esbuild_BuildOptions',
   },

[patak-cat]

Sounds good, let's merge this one in 6.1