Add setting-admin@1. Use some extra patches to achieve 5.27+ compatibility

[totten]

This adds support for setting-admin@1 (5.68's https://github.com/civicrm/civicrm-core/pull/27569).

To enable it, one runs:

civix mixin --enable=setting-admin@1

This creates the following behavior:

• Read *.setting.php for settings in this extension
• Create a permission administer {MYEXT}
• Create a route civicrm/admin/{MYEXT}
• Create a nav-item for civicrm/admin/{MYEXT}

Compatibility

I did some evaluation about version-compatibility. The original implementation of setting-admin@1 has some issues -- e.g. _ts() requires v5.64, and the chosen namespace would be problematic with the polyfill-loader (before v5.45). So I made a few updates to expand compatibility, generated a couple extensions (with this mixin), and spot-checked the admin-page on several versions (5.27, 5.39, 5.45, 5.68).

Note: There is a related update https://github.com/civicrm/civicrm-core/pull/28170. (The relative timing is not super-sensitive. But we should merge both.)

--

See also #314 (ping @mattwire).

[totten]

civibot, test this please

[totten]

civibot, test this please