Add SetExpressionCompiler for reporting v2alpha (#968)

Difference between v1 and v2:
* Treat the v2 one as a pure algorithm library. 
    * Remove proto dependency.
* The conversion from `ReportingSet.SetExpression` to
`SetExpressionCompiler.SetOperationExpression` is now done by the
caller.
* The reporting set in `setOperationExpression` has to be indexed from 0
to `numReportingSets - 1`.

src/main/kotlin/org/wfanet/measurement/reporting/service/api/v2alpha/BUILD.bazel

@@ -113,3 +113,11 @@ kt_jvm_library(
         "@wfa_consent_signaling_client//src/main/kotlin/org/wfanet/measurement/consent/client/measurementconsumer",
     ],
 )
+
+kt_jvm_library(
+    name = "set_expression_compiler",
+    srcs = ["SetExpressionCompiler.kt"],
+    deps = [
+        "@wfa_common_jvm//imports/kotlin/kotlinx/coroutines:core",
+    ],
+)