feat: (observability): trace Database.runTransactionAsync

Extracted out of PR #2158, this change traces
Database.runTransactionAsync.

Updates #2079

Author: odeke-em

observability-test/database.ts

@@ -1696,7 +1696,7 @@ describe('Database', () => {
         'Unexpected span status message'
       );
 
-      const expectedEventNames = ['Using Session', 'exception'];
+      const expectedEventNames = ['Using Session'];
       assert.deepStrictEqual(
         actualEventNames,
         expectedEventNames,

observability-test/spanner.ts

@@ -488,7 +488,7 @@ describe('EndToEnd', async () => {
         database.formattedName_
       );
       await database.runTransactionAsync(async transaction => {
-        await transaction!.run('SELECT 1');
+        const [rows] = await transaction!.run('SELECT 1');
       });
 
       traceExporter.forceFlush();

src/database.ts

@@ -3385,7 +3385,7 @@ class Database extends common.GrpcServiceObject {
             try {
               return await runner.run();
             } catch (e) {
-              setSpanErrorAndException(span, e as Error);
+              setSpanError(span, e as Error);
               throw e;
             } finally {
               span.end();