devtools: Expose introductionType to devtools clients (#38541)

in the devtools protocol, [source
forms](https://firefox-source-docs.mozilla.org/devtools/backend/protocol.html#loading-script-sources)
announced in `resources-available-array` messages can include the
`introductionType`, which more or less mirrors the field of the same
name in SpiderMonkey’s CompileOptions.

this patch exposes `introductionType` accordingly, allowing us to check
for the correct values in automated tests.

Testing: new coverage in devtools tests
Fixes: part of #36027

---------

Signed-off-by: Delan Azabani <dazabani@igalia.com>
Co-authored-by: atbrakhi <atbrakhi@igalia.com>

components/shared/devtools/lib.rs

@@ -583,6 +583,7 @@ impl fmt::Display for ShadowRootMode {
 #[derive(Debug, Deserialize, Serialize)]
 pub struct SourceInfo {
     pub url: ServoUrl,
+    pub introduction_type: String,
     pub external: bool,
     pub worker_id: Option<WorkerId>,
     pub content: Option<String>,