Interstate rendering at low zoom levels

[ZeLonewolf]

At low zoom levels, the highway network should only show Interstate highways, and not other highway=motorway.
At even lower zoom levels, the highway network should only show Interstate highways that end in a 0 or 5.
At the lowest zoom levels, shield rendering should be suppressed and the route network shown only.

Blocked by #9.

[ZeLonewolf]

At low zoom levels, highway-intense locations like New York can be quite cluttered. Suggested zoom levels based on Slack discussions:
Zoom 3-4: 1-2 digit interstates ending in 0/5
Zoom 5-6: all interstates
Zoom 7+: all highway=motorway

[ZeLonewolf]

To implement this properly, regular expression matching is required in the style layer. We would need to also deal with corner cases which use letters in interstate refs, for example:

• I-35E and I-35W in Texas should probably be treated as 2-digit interstates
• I-H* interstates in Hawaii would need to be mapped into this scheme and may be special cases.

For historical background, regex matching has been proposed for quite some time in mapbox-gl-js (mapbox/mapbox-gl-js#4089) but was never resolved. It has not been added to mapLibre.

A plugin has been developed to add regex expressions to mapbox-gl-js (https://github.com/maphubs/mapbox-gl-regex-query) which may be helpful. This library has an attribution requirement which would need to be added.

[ZeLonewolf]

OpenMapTiles 3.13 will support interstate differentiation (but not 2/3 digit separation).

[ZeLonewolf]

Fixed in #72