Bug 1726327 - Implement the new text metric type

[badboy]

The new text metric type is really just a long string,
but only allowed under specific circumstances.

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Draft while I fix outstanding things:

• glean_parser release with that metric: v4.0.0
• glean_parser update in glean.js
• schema update: #692

[badboy]

Ok, took me a moment to understand why the size check failed.
It turns out the check size once runs against the code in the current working directory.
And the second time it checks out the main branch to link in Glean, but then switches back and runs the benchmark code.

So it uses the updated benchmark code, which of course includes the changes to e.g. benchmarks/size/webext/max.js and thus fails.
It should really checkout main and run the benchmark there fully.

[brizental]

Oh, also, are you also going to do the documentation stuff under Bug 1726327? If not, please file a follow-up for that :)

[badboy]

Oh, also, are you also going to do the documentation stuff under Bug 1726327? If not, please file a follow-up for that :)

Followup bug