RUN_WITH_EXTENSION.md files - Explore the add-in code sections inaccurate

[AlexJerabek]

In every sample, there is a RUN_WITH_EXTENSION.md file. That file contains a lot of repeated content and not all of it is relevant to each project. For example, in most projects, the task pane script code is a .ts file, not a .js file. Some incorrectly refer to Excel, instead of Word. Others should also be redone to highlight specific features in the sample (like the functions folder in the custom functions sample).