fix(css): Rename inherit color to reset

What does this MR do?

Merge 1/2 for #751 (closed)

This MR aims to replace

@mixin gl-color-inherit {
  color: inherit;
}

@mixin gl-text-inherit {
  color: inherit;
}

with

@mixin gl-reset-color {
  color: inherit;
}

We also check the main GitLab project to ensure this renaming convention will not cause a regression in the project. We can see that we do have one instance of gl-color-inherit being used which we will need a MR to rename after this is released.

##Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: mr_url
  • Customers Portal: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.

Closes #751 (closed)