Export SdpTypeFromString

Needed to get rid of a form of CreateSessionDescription that is due
for deprecation.

Bug: None
Change-Id: I9717b7ded1e28cf803de4bebc852c2f255851918
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/359941
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42808}
diff --git a/api/jsep.h b/api/jsep.h
index 643a99d..2578a28 100644
--- a/api/jsep.h
+++ b/api/jsep.h
@@ -117,7 +117,8 @@
 // Returns the SdpType from its string form. The string form can be one of the
 // constants defined in SessionDescriptionInterface. Passing in any other string
 // results in nullopt.
-absl::optional<SdpType> SdpTypeFromString(const std::string& type_str);
+RTC_EXPORT absl::optional<SdpType> SdpTypeFromString(
+    const std::string& type_str);
 
 // Class representation of an SDP session description.
 //