bpo-40334: regenerate metaparser as part of regen-all

[pablogsal]

This PR does the following:

• Moves the regen-pegen target to the end of the regen-all so the changes in regen-token and are correctly picked up.
• Adds a new target regen-pegen-metaparser that regenerates the metaparser (this means also that the CI will check that this file is updated from now on)
• Adds regen-pegen-metaparser to regen-all

https://bugs.python.org/issue40334

[gvanrossum]

What brought about the desire to automatically regenerate the meta-parser?

[pablogsal]

What brought about the desire to automatically regenerate the meta-parser?

Consistency with how we handle the rest of autogenerated files to know that they are up to date, more than anything.

[gvanrossum]

Okay, sounds good.