WIP: Initial implementation of new blendfile compatibility policy.

This PR makes the following changes:
* The minfileversion stored in Blender files is now a hard limit,
  Blender does not open any file which minfileversion is newer than its
  current version.
** An error message is shown to user when trying to open such file.
** When trying to browse such file (for linking or appending), the
   FileBrowser shows an error message instead of the content of the
   library file.
* When a newer fileversion blendfile is open, a permanent warning is
  shown in the footer of the UI.
** By clicking on it, user can get more info.
** When trying to save such newer file, a popup asks for confirmation,
   with default option to 'Save As' instead.
** If 'save confirmation' option is enabled, when quiting or opening
   another file, and current one is newer, the 'Save' option is replaced
   by a 'Save As' one.

Technically, the hard check on minfileversion is implemented as a new
util in readfile code, `blo_check_minversion`, which is called as part
of the process to get a FileData (aka BlendHandle) from a file path.

The 'soft warning' about data loss due to forward compatibility
limitations is stored as a new flag in Main,
`has_forward_compatibility_issues`.

NOTE: Final commit to main (and backports to both LTSs) will happen as
several commits.

Implements #109151.

@@ -44,0 +50,4 @@
+ * 8, or 12 if subversion is provided. \param file_subversion the file subversion, if given value <
+ * 0, it is ignored, and only the `file_version` is used. */
+void BKE_blender_version_blendfile_string_from_values(char *str_buff,
+                                                      const size_t str_buff_len,

@@ -1080,1 +1083,4 @@
 
+/** Check if minversion of the file is older than current Blender, return false if it is not.
+ * Should only be called after #read_file_dna was successfuly executed. */
+static bool blo_check_minversion(FileData *fd, ReportList *reports)

@@ -458,6 +465,10 @@ int set_listbasepointers(struct Main *main, struct ListBase *lb[]);
   ((main)->versionfile < (ver) || \
    ((main)->versionfile == (ver) && (main)->subversionfile < (subver)))
 
+#define MAIN_VERSION_OLDER_OR_EQUAL(main, ver, subver) \

@@ -128,0 +138,4 @@
+                 "%d.%d.%d",
+                 file_version_major,
+                 file_version_minor,
+                 file_subversion);

@@ -128,0 +141,4 @@
+                 file_subversion);
+  }
+  else {
+    BLI_snprintf(str_buff, str_buff_len, "%d.%d", file_version_major, file_version_minor);

@@ -1080,1 +1083,4 @@
 
+/** Check if minversion of the file is older than current Blender, return false if it is not.
+ * Should only be called after #read_file_dna was successfuly executed. */
+static bool is_minversion_older_than_blender(FileData *fd, ReportList *reports)

@@ -1081,0 +1118,4 @@
+        MEM_freeN(fg);
+        return false;
+      }
+      MEM_freeN(fg);

@@ -1255,0 +1323,4 @@
+    }
+
+    BKE_reports_clear(&sfile->runtime->reports);
+    if (!BKE_blendfile_is_readable(blendfile_path, &sfile->runtime->reports)) {

@@ -29,3 +29,3 @@
 
         # Stats & Info
-        row.label(text=context.screen.statusbar_info(), translate=False)
+        layout.template_status_info()

@@ -51,0 +51,4 @@
+/**
+ * Check whether a given path is actually a readable .blend file.
+ */
+bool BKE_blendfile_is_readable(const char *path, struct ReportList *reports);

@@ -1081,0 +1087,4 @@
+{
+  BLI_assert(fd->filesdna != nullptr);
+  for (BHead *bhead = blo_bhead_first(fd); bhead; bhead = blo_bhead_next(fd, bhead)) {
+    if (bhead->code == BLO_CODE_GLOB) {

@@ -6510,0 +6533,4 @@
+  uiBut *but;
+
+  const uiStyle *style = UI_style_get();
+  uiLayout *ui_abs = uiLayoutAbsolute(layout, false);

@@ -6510,0 +6538,4 @@
+  eUIEmbossType previous_emboss = UI_block_emboss_get(block);
+
+  UI_fontstyle_set(&style->widgetlabel);
+  int width = static_cast<int>(

@@ -6510,0 +6540,4 @@
+  UI_fontstyle_set(&style->widgetlabel);
+  int width = static_cast<int>(
+      BLF_width(style->widgetlabel.uifont_id, status_info_txt, strlen(status_info_txt)));
+  width = max_ii(width, static_cast<int>(10 * UI_SCALE_FAC));

@@ -6510,0 +6597,4 @@
+                     UI_BTYPE_BUT,
+                     0,
+                     ICON_ERROR,
+                     static_cast<int>(3 * UI_SCALE_FAC),

@@ -6510,0 +6617,4 @@
+                 status_info_txt,
+                 UI_UNIT_X,
+                 0,
+                 static_cast<short>(width + UI_UNIT_X),

@@ -31,6 +31,7 @@
 #include "DNA_userdef_types.h"
 #include "DNA_workspace_types.h"
 
+#include "BKE_blender_version.h"

@@ -1245,0 +1295,4 @@
+  const bool is_asset_browser = ED_fileselect_is_asset_browser(sfile);
+  const bool is_library_browser = !is_asset_browser &&
+                                  filelist_islibrary(sfile->files, blendfile_path, nullptr);
+  if (!is_asset_browser && !is_library_browser) {

@@ -1255,0 +1324,4 @@
+
+    if (!sfile->runtime->is_blendfile_status_set) {
+      BKE_reports_clear(&sfile->runtime->is_blendfile_readable_reports);
+      sfile->runtime->is_blendfile_readable = BKE_blendfile_is_readable(

@@ -1961,6 +1961,11 @@ BlendHandle *filelist_lib(FileList *filelist)
   return filelist->libfiledata;
 }
 
+int filelist_files_num_entries(FileList *filelist)

@@ -3764,3 +3977,1 @@
-    if (WM_operator_name_call(C, "WM_OT_save_mainfile", WM_OP_EXEC_DEFAULT, nullptr, nullptr) &
-        OPERATOR_CANCELLED)
-    {
+    if (bmain->has_forward_compatibility_issues) {

@@ -3814,0 +4034,4 @@
+                                UI_BTYPE_BUT,
+                                0,
+                                0,
+                                has_forwardcompat_issues ? IFACE_("Save As...") : IFACE_("Save"),