Adds `tauri_build::try_build_context` and `ContextAttributes` for
packages that expand `tauri::generate_context!` (or a `CodegenContext`)
once and share the context with the rest of the workspace, so the
expensive context codegen re-runs only when its real inputs change
instead of on every application source edit.

The new entry point runs exactly what the context expansion consumes:
config parsing with its rerun instructions, the `dev`/`desktop`/`mobile`
cfg aliases, the OUT_DIR ACL artifacts and global API script list, and
`TAURI_ENV_TARGET_TRIPLE`. It skips application artifact staging,
executable link/deployment configuration, Android project mutation, and
the Cargo.toml feature check, which stay with the package that owns the
binary and keeps calling `build()`/`try_build`.

`ContextAttributes` carries only the ACL-shaping inputs (capabilities
path pattern, inlined plugins, app manifest, optional codegen), so
constructing it never touches the Windows attribute machinery.
Internally `acl::build` now takes those fields directly and the config
parse block is shared between both entry points; `try_build` behavior
is unchanged.