Some fixes in rendering legacy plugins

Summary:
Some exploratory testing on all iOS and Android plugins, to see how they behave inside Sandy, and fixed some layout glitches (some were also present without Sandy)

General fixes:
* Introduced some niceties like searchbox resizing properly, and toolbars wrapping automatically in Sandy, rather than buttons becoming invisible
* Containers don't grow anymore by default, but take size of contents
* ScrollContainer child is now a Layout.Vertical. Layout.Vertical should be used as default container everywhere (e.g. Tabs, Panels) in the future
* Fixed layout issue if a split container had only 1 visible child
* DetailsSidebar now scrolls vertically by default
* Details sidebar would sometimes render content in-place rather than in the reserved area
* AppSelector dropdown and Plugin list will now properly ellipse (...) if there is not enough space

Plugin fixes:
* Long database / table names in Database plugin would break layout

Also fixes https://github.com/facebook/flipper/issues/1611

Reviewed By: passy

Differential Revision: D24454188

fbshipit-source-id: c60c867270900a1d4f28587d47067c6ec1072ede

desktop/plugins/databases/index.tsx

@@ -1283,12 +1283,14 @@ export default class DatabasesPlugin extends FlipperPlugin<
                 this.state.databases[this.state.selectedDatabase - 1]?.name
               }
               onChange={this.onDatabaseSelected}
+              style={{maxWidth: 300}}
             />
             <BoldSpan style={{marginLeft: 16, marginRight: 16}}>Table</BoldSpan>
             <Select
               options={tableOptions}
               selected={this.state.selectedDatabaseTable}
               onChange={this.onDatabaseTableSelected}
+              style={{maxWidth: 300}}
             />
             <div />
             <Button onClick={this.onRefreshClicked}>Refresh</Button>