textsize detection broken when exporting to xfig

[westram]

xfig-export (=print device) has problems to properly detect the resulting size of text-elements. This results e.g. in brackets overlapping with sequence info when exporting the to xfig (see attached example xfig).

Observations:

• printing to .ps (or .pdf) reduces the effect (=less overlap)
  • for .ps this is true when exported from xfig and from arb
• effect depends on font/size-combination (for some it works perfectly, for other it fails miserably)

Possible reasons:

• ARB has no knowledge about the effective size of a text-string on the print-device
  ⇒ it can only assume the resulting size
• it only happens for non-existing font sizes
  (ARB does a fallback to next smaller existing font-size; but exports with selected font size)

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related: #721