feat(share): export the share-view codec and link-path helpers (#1419)

* feat(share): export the share-view codec for host servers

Add `@gods-eye-view/core/share/view-codec` (src/share/viewCodec.js) as a
package export with its own boundary group. The codec is pure (no DOM, no
Cesium, no external dependencies), so a host's server can decode a
/share/<code> link, for example to describe the view in link previews.

* feat(share): export the share-link address helpers

Add `@gods-eye-view/core/share/link-path` (src/share/shareLinkPath.js), so a
host's server reads /share/<code> addresses the way the app does.

changelog.d/1419-share-view-codec-export.md

@@ -0,0 +1,4 @@
+- Hosts can read share links on their server: the share-link codec and the
+  `/share/<code>` address helpers are now package exports,
+  `@gods-eye-view/core/share/view-codec` and `@gods-eye-view/core/share/link-path`
+  (samehkhamis, #1419).