RS-21330: Make label measurement div resilient to body CSS changes

Use position:fixed;width:max-content instead of display:inline-block
so the measurement div is unaffected by flex/grid parent layouts
(e.g. the new UI sets body to display:flex) and immune to global
width rules that could skew the measured label dimensions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: JustinCCYap

inst/htmlwidgets/rhtmlPictographs.js

@@ -45,7 +45,7 @@ module.exports = {
     const textDivsForEstimation = _(labels)
       .map(ensureFontSizeHasPx)
       .map(makeDivForEstimation).value()
-    const divWrapper = $(`<div id="${uniqueId}" style="display:inline-block;position:fixed;visibility:hidden">`)
+    const divWrapper = $(`<div id="${uniqueId}" style="position:fixed;visibility:hidden;width:max-content">`)
 
     divWrapper.html(textDivsForEstimation)
     $(document.body).append(divWrapper)