[Menu buttons] should menu buttons be plural or singular in the website docs left nav

[laurenmrice]

Acceptance criteria

From Michael Gower:

• As part of this implementation, the Menu button component was listed in the plural, even though the style is clearly to title each component singularly (e.g., Menu button).

Note from design:

• Code: In React we separate "Menu buttons" into their own distinct components: Menu button, Combo button, Overflow menu.
• Website and Figma: We list the 3 buttons as variants within the umbrella term of "Menu buttons", which makes it plural. If we change it to singular on the website nav and in Figma, it could get confused with the singular term "Menu button" of one of the variants.
• This is stemming from a problem with the IA of our website. Should we wait on renaming this until we revisit the IA?

[sstrubberg]

Dependent on carbon-design-system/gatsby-theme-carbon#1363

REF carbon-design-system/carbon#12947