Hard links Support Phase 1: Gofer Client dentry/inode refactor

- **Decoupled dentry and inode**: Cleanly separated dentry fields from the
file's actual metadata (permissions, size, etc.), now residing in the inode.
- **Dentry now holds inode pointer**: The dentry struct embeds a pointer to
 the shared inode, reflecting the many-to-one relationship of hard links.
- **impl logic moved to inode**: The backend-specific logic (LISA FS
 vs. Direct FS) is no longer part of the dentry struct. Instead, the
 inode struct
is extended to handle these implementations.
- **Refactored Gofer client fs**: Updated the Gofer client filesystem logic
 to work with the new dentry -> inode pointer structure.
- **Renamed files**: dentry_impl.go becomes inode_impl.go, and
{directfs/lisafs}_dentry.go are now {directfs/lisafs}_inode.go to match the
new design.
- **Disabled Save/Restore in link::IsSameFile**: Disabled save/restore in
this specific check due to complexities in maintaining inode consistency
across save/restore cycles. See comment in link.cc:45 for details.
- **New Link Tests**:
  - HardLinkChangeMode: Verifies hard link behavior, including mode changes
 across save/restore.

PiperOrigin-RevId: 750748327

Author: tranji-cloud

pkg/sentry/fsimpl/gofer/BUILD

@@ -5,6 +5,17 @@ package(default_applicable_licenses = ["//:license"])
 
 licenses(["notice"])
 
+go_template_instance(
+    name = "inode_refs",
+    out = "inode_refs.go",
+    package = "gofer",
+    prefix = "inode",
+    template = "//pkg/refs:refs_template",
+    types = {
+        "T": "inode",
+    },
+)
+
 go_template_instance(
     name = "string_list",
     out = "string_list.go",
@@ -56,16 +67,17 @@ go_template_instance(
 go_library(
     name = "gofer",
     srcs = [
-        "dentry_impl.go",
         "dentry_list.go",
-        "directfs_dentry.go",
+        "directfs_inode.go",
         "directory.go",
         "filesystem.go",
         "fstree.go",
         "gofer.go",
         "handle.go",
         "host_named_pipe.go",
-        "lisafs_dentry.go",
+        "inode_impl.go",
+        "inode_refs.go",
+        "lisafs_inode.go",
         "regular_file.go",
         "revalidate.go",
         "save_restore.go",