Correct .split() calls to only split numeric srid for ArcgisRest

[mike-000]

Fixes #12377

Ensuring the split only works for numeric srid has the advantage that the projection code can be set to a custom Arcgis SpatialReference definition (which would contain a :) without it being broken.

[ahocevar]

Currently this pull request only changes whitespace and adds newlines. Did you mean to do something else?

[mike-000]

My intention was to prevent arbitrarily splitting custom codes which are meaningful to Arcgis but do not have a numeric srid (although they do contain :) https://codesandbox.io/s/arcgis-image-forked-kuo1u?file=/main.js

[murdocha]

Does the new regex in this PR update allow a spatial reference param to be something as complex as:

{"wkt":"PROJCS[\"WGS_1984_Web_Mercator_Auxiliary_Sphere\",GEOGCS[\"GCS_WGS_1984\",DATUM[\"D_WGS_1984\",SPHEROID[\"WGS_1984\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Mercator_Auxiliary_Sphere\"],PARAMETER[\"False_Easting\",0.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",-71.68417519999998],PARAMETER[\"Standard_Parallel_1\",0.0],PARAMETER[\"Auxiliary_Sphere_Type\",0.0],UNIT[\"Meter\",1.0]]"}

(a WMAS projection with a custom central meridian around Massachusetts, US)
?
That was hard for me to visually make out without testing the code against a string like this...

Currently only a "real" EPSG code can be passed in to the OL code for ImageArcGISRest sources.
That was the initial issue I reported earlier here:
#12377

UPDATE: YES, this does seem to work with a custom projection code as shown in the codesandbox above. The work around referenced in the original issue comments also works, but this PR would also make this work (with much less effort for the next person to attempt this!)

[ahocevar]

Thanks, @mike-000.