Build and run the samples in CI, and fix the one that was already broken (#849)

Nothing built anything under Sources/Samples. That is what let SampleNet5 and
FSharpSample stay broken against the current release for seven months while
looking healthy -- pinned to 1.3.0, they compiled against a version that still
accepted integral(f, x, 1). Unpinning them in #846 was only half the fix.

Building is not enough either: both compiled cleanly and threw at runtime, so
the four console samples are run as well, about two seconds each.

Writing this found a third. FSharpPlayground already used a ProjectReference,
so nothing was concealing it -- it was broken on master, on the same call, and
no job noticed because no job ran it. Fixed here.

AngouriMathPlot and GraphicExample are built but not run, being windowed;
InteractivePlayground is built but not run because Plotly opens a browser.

Author: Rafael-SOWNet

.github/workflows/EverythingBuild.yml

@@ -37,3 +37,26 @@ jobs:
 
     - name: Build Utils
       run: dotnet build Sources/Utils/Utils/Utils.csproj
+
+    # The samples are the code most like what a user writes, and nothing built them
+    # until now. Two of them called integral(f, x, 1), which stopped parsing in 1.4.0,
+    # and stayed broken for seven months because no job compiled or ran them.
+    - name: Build samples
+      run: |
+        dotnet build Sources/Samples/SampleNet5/SampleNet5.csproj
+        dotnet build Sources/Samples/FSharpSample/FSharpSample.fsproj
+        dotnet build Sources/Samples/FSharpPlayground/FSharpPlayground.fsproj
+        dotnet build Sources/Samples/Samples/Playground.csproj
+        dotnet build Sources/Samples/InteractivePlayground/InteractivePlayground.fsproj
+        dotnet build Sources/Samples/AngouriMathPlot/AngouriMathPlot.csproj
+        dotnet build Sources/Samples/GraphicExample/GraphicExample.csproj
+
+    # Building is not enough: both samples that broke compiled cleanly and threw at
+    # runtime. Only the console ones can run here -- AngouriMathPlot and GraphicExample
+    # are windowed, and InteractivePlayground opens a browser through Plotly.
+    - name: Run console samples
+      run: |
+        dotnet run --project Sources/Samples/SampleNet5/SampleNet5.csproj --no-build
+        dotnet run --project Sources/Samples/FSharpSample/FSharpSample.fsproj --no-build
+        dotnet run --project Sources/Samples/FSharpPlayground/FSharpPlayground.fsproj --no-build
+        dotnet run --project Sources/Samples/Samples/Playground.csproj --no-build

Sources/Samples/FSharpPlayground/Program.fs

@@ -12,4 +12,4 @@ printfn "%O" (integral "x" "x2 + e")
 
 printfn "%O" (``lim x->0`` "sin(a x) / x")
 
-printfn "%O" (latex "x / e + alpha + sqrt(x) + integral(y + 3, y, 1)")
+printfn "%O" (latex "x / e + alpha + sqrt(x) + integral(y + 3, y)")