Make most text selectable

Summary:
Fix long standing issue where text by default in Flipper is not selectable. Which is super annoying when working with tables, trying to copy error messages, etc etc. Wanted to fix it with ant.design, but got so annoyed by not being able to select an error I needed, that I fixed it now :-P.

This diff makes all text selectable by default, and then bails out for specific elements, like section headers, button captions, the left toolbar (navigation) and top toolbar to preserve the desktop app look & feel.

Fixes a popular papercut issue

Changelog: All text is now selectable by default in Flipper.

Reviewed By: passy

Differential Revision: D22897793

fbshipit-source-id: 7bc50a987e012595956c07d1997959a5480790aa

desktop/plugins/seamammals/src/__tests__/seammammals.node.tsx

@@ -104,7 +104,7 @@ test('It can have selection and render details', async () => {
         style="background-image: url(http://turtle.png);"
       />
       <span
-        class="css-b2jb3d-Text"
+        class="css-8j2gzl-Text"
       >
         Turtle
       </span>