[Loading UI] Add "Memory Usage" text on the green memory usage bar.

[zyxkad]

Someone is asking about why the green loading progress bar is jumping back. To make user more clear of what they are looking for, I suggest put a text on the bar.

[3TUSK]

Technical wise, the term Heap and OffHeap shown in the screen stand for "heap memory" and "off-heap memory" respectively.

Not sure if changing them to "heap memory" is too long to fit in. "heap mem." maybe?

[HenryLoenwind]

Wasn't the amount inside the bar once or was this something I invented when I copied the bar for my mod?