exp/govulncheck: change Run to Main

Create a stable API for exp/govulncheck, for use by gopls.

The function signature for exp/govulncheck.Main should not need change
in the process of refactoring internal/govulncheck.

For golang/go#56042

Change-Id: I3c62d9bc3a3e13d80e5693cf8bcb8f8794721e0e
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/437864
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Julie Qiu <[email protected]>
Run-TryBot: Julie Qiu <[email protected]>
Reviewed-by: Julie Qiu <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>

Author: julieqiu

exp/govulncheck/govulncheck.go

@@ -12,7 +12,7 @@ import (
 // Config is the configuration for Main.
 type Config = govulncheck.Config
 
-// Run is the main function for the govulncheck command line tool.
-func Run(cfg Config) error {
+// Main is the main function for the govulncheck command line tool.
+func Main(cfg Config) error {
 	return govulncheck.Run(cfg)
 }