runtime/local: add support for idiomatic folder structures (#1963)

* runtime/local: add support for idiomatic folder structures

* runtime/local: add test coverage

* runtime/local: increase test coverage

* runtime/local: add test for empty local source

* runtime/local: make entrypoint public

runtime/local/test/bar/main.go

@@ -0,0 +1,4 @@
+// Package main is used to test the local runtime, specifically the entrypoint function
+package main
+
+func main() {}

runtime/local/test/cmd/test/main.go

@@ -0,0 +1,4 @@
+// Package main is used to test the local runtime, specifically the entrypoint function
+package main
+
+func main() {}

runtime/local/test/empty/empty.go

@@ -0,0 +1 @@
+package empty

runtime/local/test/foo/cmd/bar/main.go

@@ -0,0 +1,4 @@
+// Package main is used to test the local runtime, specifically the entrypoint function
+package main
+
+func main() {}

runtime/local/test/foo/cmd/baz/main.go

@@ -0,0 +1,4 @@
+// Package main is used to test the local runtime, specifically the entrypoint function
+package main
+
+func main() {}