Consolidate "Tools" and "Platform and Vendor Partners"

We currently list partners and platforms on two pages:

https://amp.dev/support/faq/platform-and-vendor-partners/
https://amp.dev/documentation/tools/

There are several problems with these two pages:

* There's content overlap, e.g. service providers could live on both pages.
* Tools is a misleading title as the page contains more than tools
* "Supported Platforms, Vendors and Partners" is very hard to discover as it's hidden inside the FAQ

My suggestion would be:

* Split content into:
1. Tools & CMS
2. Platforms & Partners
* Link both pages from the main navigation (e.g. move "Supported Platforms" into "About")

//cc @pbakaus @CrystalOnScript @mattludwig for thoughts