(core) move client code to core

Summary:
This moves all client code to core, and makes minimal fix-ups to
get grist and grist-core to compile correctly.  The client works
in core, but I'm leaving clean-up around the build and bundles to
follow-up.

Test Plan: existing tests pass; server-dev bundle looks sane

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2627

app/client/ui/shadowScroll.ts

@@ -0,0 +1,48 @@
+import {dom, IDomArgs, Observable, styled} from 'grainjs';
+
+// Shadow css settings for member scroll top and bottom.
+const SHADOW_TOP = 'inset 0 4px 6px 0 rgba(217,217,217,0.4)';
+const SHADOW_BTM = 'inset 0 -4px 6px 0 rgba(217,217,217,0.4)';
+
+/**
+ * Creates a scroll div used in the UserManager and moveDoc menus to display
+ * shadows at the top and bottom of a list of scrollable items.
+ */
+export function shadowScroll(...args: IDomArgs<HTMLDivElement>) {
+  // Observables to indicate the scroll position.
+  const scrollTop = Observable.create(null, true);
+  const scrollBtm = Observable.create(null, true);
+  return cssScrollMenu(
+    dom.autoDispose(scrollTop),
+    dom.autoDispose(scrollBtm),
+    // Update scroll positions on init and on scroll.
+    (elem) => { setTimeout(() => scrollBtm.set(isAtScrollBtm(elem)), 0); },
+    dom.on('scroll', (_, elem) => {
+      scrollTop.set(isAtScrollTop(elem));
+      scrollBtm.set(isAtScrollBtm(elem));
+    }),
+    // Add shadows on the top/bottom if the list is scrolled away from either.
+    dom.style('box-shadow', (use) => {
+      const shadows = [use(scrollTop) ? null : SHADOW_TOP, use(scrollBtm) ? null : SHADOW_BTM];
+      return shadows.filter(css => css).join(', ');
+    }),
+    ...args
+  );
+}
+
+// Indicates that an element is currently scrolled such that the top of the element is visible.
+function isAtScrollTop(elem: Element): boolean {
+  return elem.scrollTop === 0;
+}
+
+// Indicates that an element is currently scrolled such that the bottom of the element is visible.
+// It is expected that the elem arg has the offsetHeight property set.
+function isAtScrollBtm(elem: HTMLElement): boolean {
+  return elem.scrollTop >= (elem.scrollHeight - elem.offsetHeight);
+}
+
+const cssScrollMenu = styled('div', `
+  flex: 1 1 0;
+  width: 100%;
+  overflow-y: auto;
+`);