Implement MySQL Spatial Types

[itsbalamurali]

Based on the geo-types crate implemented support for Spatial Data Types for sqlx-mysql crate under spatial-data-types feature flag.

Is this a breaking change?

No.

If yes, this pull request will need to wait for the next major release (0.{x + 1}.0)

Behavior changes can be breaking if significant enough.
Consider Hyrum's Law:

With a sufficient number of users of an API,
it does not matter what you promise in the contract:
all observable behaviors of your system
will be depended on by somebody.

[abonander]

Closing because this is still marked as draft 3 months later. Feel free to open a new PR if you ever get back to this.