pmtilesRules fails with missing protomapsL global variable

[prushforth]

This bug was introduced by the transition to full es modules (I think).

The solution is to manually (conditionally) create the protomapsL global before importing the pmtilesRules for a layer, which currently sometimes fails, because for example simply designating a theme does not avail itself of the protomapsL variable symbols, but creating custom symbolizers does indeed rely on those exports.

Needs a test, which means it needs some spearfish mvt files save to test/data to test with.