Address @ts-expect-error

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Address occurrences of @ts-expect-error.

Then make this change in package.json:

-              "ts-expect-error": "allow-with-description",
+              "ts-expect-error": true

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Unassigning until we're working on this sim.

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As of this writing, all files have been converted to TypeScript.

There are 17 occurrences of @ts-expect-error, all in view code, and all related to the same problem:

In Challenge.ts, we have guessProperty: Property<Line | NotALine>, because the user's guess (which can consist of up to 3 points) may not be a valid line. This causes problems with the many places where we are expecting Property<Line>. Note that the NotALine case occurs only in the "Place The Points" challenge type, where the user must place 3 points on the graph.

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There are now 14 occurrences of @ts-expect-error, all in graphing-lines/js/linegame/view/, and all with this description:

// @ts-expect-error guessProperty is Property<Line | NotALine>

PlaceThePoints is the only challenge where NotALine is relevant. In PlaceThePoints.ts, line 64:

    // Update the guess when the points change.
    // unmultilink unnecessary because PlaceThePoints owns these Properties.
    Multilink.multilink(
      [ this.p1Property, this.p2Property, this.p3Property ],
      ( p1, p2, p3 ) => {
        const line = new Line( p1.x, p1.y, p2.x, p2.y, LineGameConstants.GUESS_COLOR );
        if ( line.onLinePoint( p3 ) ) {
          // all 3 points are on a line
          this.guessProperty.value = line;
        }
        else {
          // the 3 points don't form a line
64        this.guessProperty.value = new NotALine();
        }
      } );

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In the above commits, I added this cast to address challenge.guessProperty:

assert && assert( challenge.guessProperty.value instanceof Line );
const guessProperty = challenge.guessProperty as Property<Line>;

Then I realized that this is unsafe, because the cast is only valid for the initial value of guessProperty. So I reverted.

There are also some Color | string => TColor changes in the above commits that are valid, and have been kept.

I also made LineNode take lineProperty: Property<Line> | Property<Line | NotALine>, so we're down to 12 uses of @ts-expect-error.

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In the above commit, I replaced a few more unsafe as casts with @ts-expect-error.

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In the above commits, I simplified lineProperty: Property<Line> | Property<Line | NotALine> to lineProperty: Property<Line | NotALine> in the above commits.

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Unassigning until work on this sim resumes.

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This does not need to be completed for the 1.4 release, #142.