Use enumerations instead of simple integer constants in order to be able to store the surface types internally under different IDs than the corresponding API values.

Check whether values corresponding to the surface types can be reliably written and retrieved from the storage. The test currently fails because the number of different surface types exceeds the available data type range of 4 bits.

Remove some less common and relevant surface types such as "woodchips", or ambiguous ones: "fine gravel" and "cobblestone" in order to be able to encode them as 4-bit values. Note that "woodchips" has never been functional because its original value of 16 exceeds the available data type range of 4 bits.

Improves code readability and potentially performance.

Address issue reported by sonarcloud by replacing calls to `com.graphhopper.storage.Directory#find(java.lang.String)` by `com.graphhopper.storage.Directory#create(java.lang.String)`

According to OSM wiki `surface=earth` is a synonym of `surface=dirt` and is used for where surface is exposed earth/soil/dirt but it is not sand or gravel or rock.

Ways labelled with OSM tag `surface` set to "unhewn_cobblestone", "bricks" or "brick" are classified as surface type "Paving Stones" rather than "Unknown".

Ways labelled with OSM tag `surface` set to "rock", "rocks", "stone", "shells" or "salt" are classified as surface type "Unpaved" rather than "Unknown".

Ways labelled with OSM tag `surface` set to "chipseal", "bitmac" or "tarmac" are classified as surface type "Asphalt" rather than "Unknown". According to OSM wiki most of chipseal and bitmac surfaces are likely tagged as `surface=asphalt`, whereas `surface=tarmac` is often incorrectly used for asphalt/concrete surfaces as actual tarmacadam is very unusual.

Ways labelled with OSM tag `surface` set to "soil" are classified as surface type "Dirt" rather than "Unknown".

…crete"

According to OSM wiki `surface=cement` is often used, by mistake, instead of `surface=concrete`.

Road classification doesn't necessarily imply surface. For example, driveways which are supposed to be tagged as `highway=service` + `service=driveway` are in many cases not paved.