Add line_substring linear referencing function to expression engine

[qgib]

Author Name: Nikolay Lebedev (Nikolay Lebedev)
Original Redmine Issue: 15611

Redmine category:expressions

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It's cool that we now have line_interpolate_point() function in expression engine. It would be really nice to have a similar function that returns a substring of a linestring (analogue to postgis st_line_substring()).
This should improve line styling and labelling possibilities.

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• easy_fix was configured as 0

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

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Applied in changeset a4386d6.

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• done_ratio was changed from 0 to 100
• status_id was changed from Open to Closed

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• resolution was changed from to fixed/implemented
• description was changed from It's cool that we now have line_interpolate_point() function in expression engine. It would be really nice to have a similar function that returns a substring of a linestring (analogue to postgis st_line_substring()).
  This should improve line styling and labelling possibilities. to It's cool that we now have line_interpolate_point() function in expression engine. It would be really nice to have a similar function that returns a substring of a linestring (analogue to postgis st_line_substring()).
  This should improve line styling and labelling possibilities.