(core) Add a button and a tooltip to Access Rules page item, in View-As mode.

Summary:
- When in View-As mode, clicking the Access Rules page now shows a tooltip
  with a link to return to normal mode and open the Access Rules page.
- A "revert" button is shown next to the item with the same behavior.
- Implemented hoverTooltip() with various options. (It will have other uses.)
- Simplify creation of links based on UrlState:
  - Allow merging with previous urlState using a function
  - Add a helper function to merge in aclAsUser parameter.
  - Add setHref() method to UrlState

Test Plan:
Added test cases:
  - for tooltips generally in test/projects
  - for updating UrlState using a callback
  - for Access Rules tooltip and button behavior

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2749

app/client/ui/LeftPanelCommon.ts

@@ -131,19 +131,6 @@ export const cssPageLink = styled('a', `
   }
 `);
 
-// Styled like a cssPageLink, but in a disabled mode, without an actual link.
-export const cssPageDisabledLink = styled('span', `
-  display: flex;
-  align-items: center;
-  height: 32px;
-  line-height: 32px;
-  padding-left: 24px;
-  outline: none;
-  text-decoration: none;
-  outline: none;
-  color: inherit;
-`);
-
 export const cssLinkText = styled('span', `
   white-space: nowrap;
   overflow: hidden;