Add PoundPerSquareFoot and PoundPerThousandSquareFeet (#1638)

Standard for paper grammage/base weight in North America is lbs/MSF
(pound per 1000 square feet) instead of g/m².
Conversion factor is standardized by TAPPI (free sample of TIP 0800-01
can be found
[here](https://www.normsplash.com/Samples/TAPPI/145775521/TAPPI-TIP-0800-01-2012-en.pdf)).

I also added lbs/ft² for completeness.

---------

Co-authored-by: Andreas Fischer <andreasfische@bhs-intralogistics.com>
Co-authored-by: Andreas Gullberg Larsen <andreas.larsen84@gmail.com>

Author: 3 people

.agents/criteria-for-adding-quantities-and-units.md

@@ -22,6 +22,13 @@ Ask for justification and use cases if this is not clear.
 - [x] Can be converted to other units of the same quantity
 - [x] The conversion function is well established without ambiguous competing standards
 
+### Review test values for new units
+
+- [x] Test values use literal constants, not expressions that repeat the JSON conversion functions
+- [x] Test values preferably cite a verifiable source, such as an online converter, standard, or reference table
+- [x] Test values have at least 7 significant figures where possible, but no more precision than `double` can usefully represent
+- [x] The expected value independently sanity-checks the conversion function instead of mirroring its implementation
+
 ### Avoid X-per-Y units
 
 There are many variations of unit A over unit B, such as `LengthPerAngle` and we want to avoid adding these unless they are very common.

Common/UnitDefinitions/AreaDensity.json

@@ -56,6 +56,38 @@
           "Abbreviations": [ "mg/m²" ]
         }
       ]
+    },
+    {
+      "SingularName": "PoundPerSquareFoot",
+      "PluralName": "PoundsPerSquareFoot",
+      "BaseUnits": {
+        "L": "Foot",
+        "M": "Pound"
+      },
+      "FromUnitToBaseFunc": "{x} * (0.45359237 / 0.09290304)",
+      "FromBaseToUnitFunc": "{x} / (0.45359237 / 0.09290304)",
+      "Localization": [
+        {
+          "Culture": "en-US",
+          "Abbreviations": [ "lb/ft²", "lbs/ft²", "lb/SF", "lbs/SF" ]
+        }
+      ]
+    },
+    {
+      "SingularName": "PoundPerThousandSquareFeet",
+      "PluralName": "PoundsPerThousandSquareFeet",
+      "BaseUnits": {
+        "L": "Foot",
+        "M": "Pound"
+      },
+      "FromUnitToBaseFunc": "{x} * (0.45359237 / 0.09290304) / 1000",
+      "FromBaseToUnitFunc": "{x} / (0.45359237 / 0.09290304) * 1000",
+      "Localization": [
+        {
+          "Culture": "en-US",
+          "Abbreviations": [ "lb/MSF", "lbs/MSF", "lb/1000ft²", "lbs/1000ft²", "lbm/MSF" ]
+        }
+      ]
     }
   ]
 }

Common/UnitEnumValues.g.json

@@ -86,7 +86,9 @@
   "AreaDensity": {
     "KilogramPerSquareMeter": 1,
     "GramPerSquareMeter": 6,
-    "MilligramPerSquareMeter": 10
+    "MilligramPerSquareMeter": 10,
+    "PoundPerThousandSquareFeet": 3,
+    "PoundPerSquareFoot": 8
   },
   "AreaMomentOfInertia": {
     "CentimeterToTheFourth": 1,

UnitsNet.NumberExtensions.CS14.Tests/GeneratedCode/NumberToAreaDensityExtensionsTest.g.cs

@@ -34,6 +34,12 @@ public class AreaDensityTests : AreaDensityTestsBase
 
         protected override double MilligramsPerSquareMeterInOneKilogramPerSquareMeter => 1000000;
 
+        /// <summary>https://www.kylesconverter.com/area-density/kilograms-per-square-meter-to-pounds-per-square-foot</summary>
+        protected override double PoundsPerSquareFootInOneKilogramPerSquareMeter => 0.20481614362252172;
+
+        /// <summary>https://www.kylesconverter.com/area-density/grams-per-square-meter-to-pounds-per-thousand-square-feet</summary>
+        protected override double PoundsPerThousandSquareFeetInOneKilogramPerSquareMeter => 204.81614362252172;
+
         [Fact]
         public void AreaDensityTimesAreaEqualsMass()
         {