Flatten the folder structure of components

[janechu]

Abstract

There has been some inconsistency when structuring the src folders of components where sometimes a flat structure is used for items related to each other (menu and menu-item) and sometimes a nested folder structure is used (accordion and accordion-item).

These should use a consistently flat structure since nesting can sometimes be subjective.

Requirements

Change the folder structure in the packages/web-components/fast-components/src/ and packages/web-components/fast-foundation/src/ folders from:

/accordion
    /accordion-item
/progress
    /progress
    /progress-ring
/tabs
    /tab
    /tab-panel

to:

/accordion
/accordion-item
/progress
/progress-ring
/tabs
/tab
/tab-panel

[rimildeyjsr]

@janechu @chrisdholt - can I work on this?

[janechu]

@rimildeyjsr go for it!