Fix: Migrating every theme to TypeScript.

[tgbhy]

The basics

• I validated my changes

The details

Resolves

Fixes #2158

Proposed Changes

Migrate every theme sample to TypeScript.

Reason for Changes

It would be usable in TypeScript like explained in the fixed issue.

Test Coverage

Manually tested with a Windows 10 PC and Brave Browser.
I tested on using a default installation of Blockly and recreating the schema of each readme-media/Theme.png

[google-cla]

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[cpcallen]

Hi @tgbhy. Thanks for this useful PR! The changes look good but there are some additional steps needed before we can accept the PR:

• You'll need to agree to the CLA.
• eslint is unhappy about all the properties with underscores in their name. You'll need to disable this rule for these declarations.
• You'll also need to run npm run format to run Prettier and thereby fix the formatting.