fix: multi /pkg/<module> in dlv debugging

This issue is copied from my PR: https://github.com/cockroachdb/rules_go/pull/18

When I try to debug cockroach with VSCode, I found some bugs when I try to set breakpoints.
VSCode tells me that some files cannot be found in dlv sources, even if I use this to substitute the path to package path:
``` json
{
"from": "${workspaceFolder}",
"to": "github.com/cockroachdb/cockroach"
},
```
One of the cases is `/pkg/gossip/gossip.go`
When using `dlv` as follows:
```shell
dlv exec ../_bazel/bin/pkg/cmd/cockroach/cockroach_/cockroach -- start --insecure --store=node1 --listen-addr=localhost:26257 --http-addr=localhost:8080 --join=localhost:26257,localhost:26258,localhost:26259
```
and then use `sources` command to list all sources. You can find its path like this:

`github.com/cockroachdb/cockroach/pkg/gossip/pkg/gossip/gossip.go`
The relpath `pkg/gossip` has been appended twice.

This problem is associated with one issue in cockroach:
https://github.com/cockroachdb/cockroach/issues/64379
You modified complilepkg.go as follows:
```go
// We want the source files to show up (e.g. in stack traces) with the package
// path. We use -trimpath to replace the root path with the correct prefix
// of the package path.
root := abs(".")
relSrcPath, err := filepath.Rel(root, srcs.goSrcs[0].filename)
if err != nil {
return err
}
rootPkgPath := filepath.Clean(strings.TrimSuffix(packagePath, filepath.Dir(relSrcPath)))
gcFlags = append(gcFlags, fmt.Sprintf("-trimpath=%s=>%s", root, rootPkgPath))
```
But when you debug bazel, you can get the command passed bazel looks like this:
```
bazel-out/k8-opt-exec-ST-13d3ddad9198/bin/external/go_sdk/builder_reset/builder compilepkg
-sdk external/go_sdk -installsuffix linux_amd64 -tags bazel,gss,bazel,gss
-src bazel-out/k8-dbg/bin/foo/foo_go_proto_/example.com/foo/foo.pb.go
-src foo/foo.go -embedroot bazel-out/k8-dbg/bin -embedroot ''
-embedlookupdir foo/foo_go_proto_/example.com/foo -embedlookupdir foo
(serveral arcs)
-importpath heyhey -p example.com/foo -package_list bazel-out/k8-opt-exec-ST-13d3ddad9198/bin/external/go_sdk/packages.txt -o bazel-out/k8-dbg/bin/foo/foo.a -x bazel-out/k8-dbg/bin/foo/foo.x -gcflags '-N -l' -asmflags '')
```
The first src is the protobuf file and therefore `srcs.goSrcs[0].filename` is `bazel-out/k8-dbg/bin/foo/foo_go_proto_/example.com/foo/foo.pb.go`, but we are expecting the source file which is not generated.

so I modify this part as follows:
```go
srcFullPath := srcs.goSrcs[0].filename
for _, goSrc := range srcs.goSrcs {
if !strings.HasSuffix(goSrc.filename, ".pb.go") {
srcFullPath = goSrc.filename
break
}
}
relSrcPath, err := filepath.Rel(root, srcFullPath)
```
Once srcs has source code which is not generated, we use its path.
Then problem is fixed, and we get its path in `dlv` as follows:
`github.com/cockroachdb/cockroach/pkg/gossip/gossip.go`

Jira issue: CRDB-36174