Rename Label.Bp_text to OriginalModuleName.

OriginalModuleName is a clearer name for what the field represents.

Also document it.

Follow-up from aosp/1675466.

Test: TH
Change-Id: Ie1152b5ae63f388164582be70e193a91ef96c89c
diff --git a/genrule/genrule.go b/genrule/genrule.go
index 3a9aecc..77dae75 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -856,8 +856,8 @@
 			cmd = strings.Replace(cmd, "$(locations)", fmt.Sprintf("$(locations %s)", tools.Value.Includes[0].Label), -1)
 		}
 		for _, l := range allReplacements.Includes {
-			bpLoc := fmt.Sprintf("$(location %s)", l.Bp_text)
-			bpLocs := fmt.Sprintf("$(locations %s)", l.Bp_text)
+			bpLoc := fmt.Sprintf("$(location %s)", l.OriginalModuleName)
+			bpLocs := fmt.Sprintf("$(locations %s)", l.OriginalModuleName)
 			bazelLoc := fmt.Sprintf("$(location %s)", l.Label)
 			bazelLocs := fmt.Sprintf("$(locations %s)", l.Label)
 			cmd = strings.Replace(cmd, bpLoc, bazelLoc, -1)