Fix ArcGISTiledElevationTerrainProvider TypeScript definition

[mramato]

#9465 (comment)

There was no new line after the WebGLConstants enum definition in the TypeScript definition file:

...
    MAX_TEXTURE_MAX_ANISOTROPY_EXT = 34047
}/**
 * A {@link TerrainProvider} that produces terrain geometry by tessellating height maps
...

This caused ArcGISTiledElevationTerrainProvider to not be completely picked up by the TypeScript compiler. There's special handling from WebGLConstants to hoist it to the top of the file, so we just needed to insert two new lines in the special handling code to fix the problem:

...
    MAX_TEXTURE_MAX_ANISOTROPY_EXT = 34047
}

/**
 * A {@link TerrainProvider} that produces terrain geometry by tessellating height maps
...

[cesium-concierge]

Thanks for the pull request @mramato!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[mramato]

To test this, just run build-ts and compare it to master and you'll see that the new line is inserted as described above.

[mramato]

Self merging this so that I can start the release.