[5.5] Geospatial improvements

[paulofreitas]

• Adds missing spatial columns support to SQL Server driver
• Adds missing spatial index support to other drivers than MySQL
• Adds missing spatial index dropping support
• Misc improvements to geospatial support

Since it ended up being big I pushed the commits without squashing them to ease reviewing what have changed. 👍

Added 18 new tests and 39 assertions to the test suite.

Notes

I was going do add full SpatiaLite support to the SQLite driver, then I realized that unfortunately the PDO SQLite driver does not support loading SQLite extensions at all, only the PHP SQLite3 extension. 😞

Note that since SQLite data types are dynamic it does make sense to support spatial column types as already implemented. 😉

[taylorotwell]

I don't like that you changed so many comments, formatting, and unrelated things. I can barely tell what is going on because of all the noise in this PR.

[paulofreitas]

I've rebased discarding some code simplifications I did previously. Now only the last commit change stuff, and it's easier to review it isolated from the others.

Regarding the last commit, it just...

• Improves grammars' docstrings and method names for spatial column types (this does not break anything, it's just to follow the convention used within other methods)
• Improves grammars exception type/message for unsupported spatial features
• Standardizes spatial features tests across all drivers (i. e. makes them similar)

All tests passed. Hope it's easier to review now. 😄

[antonkomarev]

@paulofreitas thank you for improving Geo functionality!