(core) Fix issue with lodash's map interpreting objects with length as array-like

Summary:
Here's a series of badness that easily leads to a crash, in reverse order:
- Lodash's map() function interprets an object with a .length property as an array.
- Some very old code generated human-friendly descriptions of user actions,
  applying map() to parts of them. It so happens that this generated description
  isn't even used.
- If a user action is encountered with a sufficiently large length propery,
  map() would exhaust the server memory.

Fixed by removing old unneeded code, and replacing some other occurrences of
lodash's map() with native equivalents.

Test Plan: Tested manually on a local reproduction of the issue.

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D3938

app/common/ThemePrefs-ti.ts

@@ -185,6 +185,8 @@ export const ThemeColors = t.iface([], {
   "left-panel-page-options-selected-hover-bg": "string",
   "left-panel-page-initials-fg": "string",
   "left-panel-page-initials-bg": "string",
+  "left-panel-page-emoji-fg": "string",
+  "left-panel-page-emoji-outline": "string",
   "right-panel-tab-fg": "string",
   "right-panel-tab-bg": "string",
   "right-panel-tab-icon": "string",