Add area_thresh to COMMON_OPTIONS (#1426)

* update pygmt/helpers/decorators.py
* update docstring in coast

Co-authored-by: Meghan Jones <meghanj@alum.mit.edu>
Co-authored-by: Wei Ji <23487320+weiji14@users.noreply.github.com>

Author: 3 people

pygmt/helpers/decorators.py

@@ -25,6 +25,14 @@
             *Required if this is the first plot command*.
             *projcode*\[*projparams*/]\ *width*.
             Select map :doc:`projection </projections/index>`.""",
+    "A": r"""
+        area_thresh : int or float or str
+            *min_area*\ [/*min_level*/*max_level*][**+a**\[**g**\|\ **i**]\
+            [**s**\|\ **S**]][**+l**\|\ **r**][**+p**\ *percent*].
+            Features with an area smaller than *min_area* in km\ :sup:`2` or of
+            hierarchical level that is lower than *min_level* or higher than
+            *max_level* will not be plotted [Default is 0/0/4 (all
+            features)].""",
     "B": r"""
         frame : bool or str or list
             Set map boundary

pygmt/src/coast.py

@@ -65,12 +65,7 @@ def coast(self, **kwargs):
     ----------
     {J}
     {R}
-    area_thresh : int, float, or str
-        *min_area*\ [/*min_level*/*max_level*][**+a**\[**g**\|\ **i**]\
-        [**s**\|\ **S**][**+l**\|\ **r**][**+p**\ *percent*].
-        Features with an area smaller than *min_area* in km\ :sup:`2` or of
-        hierarchical level that is lower than *min_level* or higher than
-        *max_level* will not be plotted.
+    {A}
     {B}
     lakes : str or list
         *fill*\ [**+l**\|\ **+r**].