tooltips: Fix hotkey-hint CSS class reuse.

The "hotkey-hint" class name used internally in
d66f2d900f conflicted with the
preexisting class name for hotkey hints into popovers, introduced in
80ff3d8da5.

Given that the new class is for a styling of hotkey hints designed for
use in tooltips, it was a bad name anyway, so just rename it to
tooltip-hotkey-hint. We rename the related cluster of variable names
to match this.

webpack.config.ts

@@ -143,7 +143,7 @@ export default (env: {minimize?: boolean} = {}, argv: {mode?: string}): webpack.
                             "t",
                             "tr",
                             "rendered_markdown",
-                            "hotkey_hints",
+                            "tooltip_hotkey_hints",
                         ],
                         preventIndent: true,
                     },