feat(css/prefixer): Fix default implementation (#10351)

**Related issue:**

 - swc-project/plugins#437

Author: kdy1

Diff for: .changeset/thick-experts-count.md

@@ -0,0 +1,6 @@
+---
+swc_core: patch
+swc_css_prefixer: patch
+---
+
+feat(es/preset-env): Make `browserslist` file support opt-in

Diff for: crates/swc_css_prefixer/src/options.rs

@@ -2,7 +2,7 @@ use preset_env_base::query::Query;
 pub use preset_env_base::query::Targets;
 use serde::Deserialize;
 
-#[derive(Debug, Default, Clone, Deserialize)]
+#[derive(Debug, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]
 #[serde(deny_unknown_fields)]
 pub struct Options {
@@ -13,3 +13,11 @@ pub struct Options {
 fn default_targets() -> Option<Targets> {
     Some(Targets::Query(Query::Single("".into())))
 }
+
+impl Default for Options {
+    fn default() -> Self {
+        Self {
+            env: default_targets(),
+        }
+    }
+}

Diff for: crates/swc_css_prefixer/tests/prefixer.rs

@@ -63,7 +63,7 @@ fn prefix(input: PathBuf, options: Options, suffix: Option<&str>) {
 
 #[testing::fixture("tests/fixture/**/input.css")]
 fn test_without_env(input: PathBuf) {
-    prefix(input, Options::default(), None)
+    prefix(input, Options { env: None }, None)
 }
 
 #[testing::fixture("tests/fixture/**/input.css")]