[MIGRATION] pegasus.forms migrations

[wjordan]

This PR contains 2 Pegasus migrations affecting the forms table:

130. Add JSON generated column with secondary index for country-code attribute to improve query performance.
131. Convert data JSON columns to native JSON data type for optimized performance and storage.
     Requires MySQL >= 5.7.13.

Since this PR depends on #22771, the diff will include those changes until the other PR is merged, so see c1cfab2d68350b75bc7594a3cce92e94014142b6 for the commit containing only this PR's changes. [done]

MySQL DDL generated by these migrations:

# 130.
ALTER TABLE `forms` ADD COLUMN `location_country_code_s` char(2) GENERATED ALWAYS AS (processed_data->>"$.location_country_code_s")
CREATE INDEX `forms_kind_location_country_code_s_index` ON `forms` (`kind`, `location_country_code_s`)

# 131.
ALTER TABLE `forms` CHANGE COLUMN `data` `data` JSON NOT NULL, CHANGE COLUMN `processed_data` `processed_data` JSON NULL

[wjordan]

Currently depends on #22771, which fixes the issue with generated columns being included in the update query in form_helper. [merged]