Type annotations (#4789)

* add some types to XAxisModel

* some more type defs and small code tweaks while getting familiar with plots

* more type annotations and a few small tweaks

* more type annotations and small tweaks to make types show

* add mocha types

* Add karma and jasmine, too

* further simplify plot canvas creation

* further simplify plot canvas creation

* update types, avoid runtime behavior in type definition that breaks SeriesCollection

* undo the changes to MctChart, improve it later

* lint fix

Co-authored-by: unlikelyzero <jchill2@gmail.com>
Co-authored-by: John Hill <john.c.hill@nasa.gov>
Co-authored-by: Jamie V <jamie.j.vigliotta@nasa.gov>

src/plugins/plot/MctPlot.vue

@@ -661,7 +661,7 @@ export default {
             this.positionOverElement = {
                 x: event.clientX - this.chartElementBounds.left,
                 y: this.chartElementBounds.height
-              - (event.clientY - this.chartElementBounds.top)
+                    - (event.clientY - this.chartElementBounds.top)
             };
 
             this.positionOverPlot = {