Always invalidate yardstick measurements when the editor becomes visible

...because content could get reflowed and previous measurements might
become inaccurate. Typically, this could occur when measuring while the
editor is hidden: in that case, the yardstick would always report `0px`
and save that position into the cache. Then, when the editor becomes
visible again, the wrong `0px` value would be returned, thus causing
cursors etc. to be displayed incorrectly.

This was being shadowed by a bug in our measurements cache, but after
fixing it in #12730 it started becoming evident.

src/text-editor-component.coffee

@@ -195,9 +195,10 @@ class TextEditorComponent
 
   becameVisible: ->
     @updatesPaused = true
-    if @invalidateMeasurementsWhenVisible
-      @invalidateMeasurements()
-      @invalidateMeasurementsWhenVisible = false
+    # Always invalidate LinesYardstick measurements when the editor becomes
+    # visible again, because content might have been reflowed and measurements
+    # could be outdated.
+    @invalidateMeasurements()
     @measureScrollbars() if @measureScrollbarsWhenShown
     @sampleFontStyling()
     @sampleBackgroundColors()
@@ -937,11 +938,8 @@ class TextEditorComponent
     @invalidateMeasurements()
 
   invalidateMeasurements: ->
-    if @isVisible()
-      @linesYardstick.invalidateCache()
-      @presenter.measurementsChanged()
-    else
-      @invalidateMeasurementsWhenVisible = true
+    @linesYardstick.invalidateCache()
+    @presenter.measurementsChanged()
 
   screenPositionForMouseEvent: (event, linesClientRect) ->
     pixelPosition = @pixelPositionForMouseEvent(event, linesClientRect)