typescript: Add overrides where necessary for stricter environments.

[schwehr]

PR created with:

cd js

perl -pi -e 's/^(?<space>\s+)(?<func>render\(\))/$+{space}override $+{func}/g' *.ts
perl -pi -e 's/^(?<space>\s+)static styles/$+{space}static override styles/g' *.ts

perl -pi -e 's/title\: string \=/override title\: string \=/g' container.ts legend_customization.ts
perl -pi -e 's/title =/override title \=/g' legend.ts
perl -pi -e 's/tabIndex\: number/override tabIndex\: number/g' legend.ts 

perl -pi -e 's/^(?<space>\s+)updated\(/$+{space}override updated\(/g' *.ts

perl -pi -e 's/^(?<space>\s+)onCustomMessage/$+{space}override onCustomMessage/g' layer_editor.ts lit_widget.ts
perl -pi -e 's/^(?<space>\s+)connectedCallback/$+{space}override connectedCallback/g'  raster_layer_editor.ts