file.importProject: import an EffectCraft project into the open project

File > Import > EffectCraft Project (and .ecproj/.ecprojx given to File > Import)
merges the project into a folder named after the file, with every id shifted past
the open project's, in one undo step. Relative footage resolves next to the file;
the result lists comps, root comps, primaryComp and missing media.

offset_ids now shifts tracker Motion Targets and saturates instead of overflowing;
fix_next_id saturates too, so a damaged file can't overflow on open or import.
Menu entry translated in all ten menu catalogues.

Rebased onto current upstream main for the split of #858 (test module list in
engine lib.rs; es/pt-br/ru/fr/de/cs menu translations).

(cherry picked from commit 19c653fccc95133fb35e978a7f7f20a18c0e8c89)
(cherry picked from commit 4e751ad2)

(cherry picked from commit ceed706cc3b5f3755769738a1ddb3d965a94ab6b)

docs/parity-log.md

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+
+## Update: File ▸ Import ▸ EffectCraft Project
+
+- **Import a project into a project**, as After Effects imports an `.aep`:
+  `file.importProject {path}` (File ▸ Import ▸ EffectCraft Project..., and `.ecproj` /
+  `.ecprojx` files given to File ▸ Import) merges the project into a folder named after the
+  file. Every item, layer and property id moves past the open project's, so references
+  (precomps, parents, track mattes, Layer Control values, Essential Graphics, tracker
+  targets) stay intact. It's one undo step. Footage paths relative to the imported project
+  resolve next to it. The result lists the comps, the root comps, `primaryComp` (the only
+  root comp) and missing media.
+- Id shifting saturates instead of overflowing on damaged files, for both templates and
+  projects.