Install cross partition symlinks in autogenerated vendor.img

These match the symlinks present in the kati built vendor.img file.

Since structs are not supported in `generateBpContent`, Android.bp
generation for vendor is skipped for now.

Bug: 374371755
Test: Verified that odm and lib/modules are present in vendor.img's
fileList for aosp_cf_x86_64_phone

Change-Id: I2564d23a5fc3b8e1aad360373ff2c103a074cfe7
diff --git a/filesystem/filesystem.go b/filesystem/filesystem.go
index ca0a7f7..97421c8 100644
--- a/filesystem/filesystem.go
+++ b/filesystem/filesystem.go
@@ -66,7 +66,7 @@
 	entries []string
 }
 
-type symlinkDefinition struct {
+type SymlinkDefinition struct {
 	Target *string
 	Name   *string
 }
@@ -111,7 +111,7 @@
 	Dirs proptools.Configurable[[]string]
 
 	// Symbolic links to be created under root with "ln -sf <target> <name>".
-	Symlinks []symlinkDefinition
+	Symlinks []SymlinkDefinition
 
 	// Seconds since unix epoch to override timestamps of file entries
 	Fake_timestamp *string