Convert theme plugins to ts

[tgbhy]

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Component

Themes (like @blocky/theme-dark)

Description

There is no index.d.ts in module so we can't import it with Typescript (or we need to use //@ts-ignore)

Reproduction steps

1. Prepare a typescript project
2. Install the package named "@blockly/theme-dark"

Stack trace

[tsl] ERROR in C:\Users\user\Desktop\blocksk-typescript\src\index.ts(8,23)
      TS7016: Could not find a declaration file for module '@blockly/theme-dark'. 'C:\Users\esteb\Desktop\blocksk-typescript\node_modules\@blockly\theme-dark\dist\index.js' implicitly has an 'any' type.
  Try `npm i --save-dev @types/blockly__theme-dark` if it exists or add a new declaration (.d.ts) file containing `declare module '@blockly/theme-dark';`

Screenshots

[maribethb]

Hello, we've recently converted some of the plugins to TypeScript, but not all of them have been migrated. The themes should be pretty straightforward to migrate if you'd like to contribute a patch. You can copy a tsconfig out of any of the other plugins. Otherwise, this is in our backlog but we are not able to prioritize it in the coming quarter. Thanks!