Normalize num type

[tlserver]

1. CustomPoint<int> is not used in this plugin explicitly: change CustomPoint to always double to avoid potential error.
2. Some property are num and some are double, but seem having no good reason: change to double for consistency.
3. mapState.nonrotatedSize and mapState.size is always available after widget initlized: change its getter to non-nullable.
4. CustomPoint.multiplyBy() have same functionality as operator *: make as deprecated.

[TesteurManiak]

(cc @JaffaKetchup)

[JaffaKetchup]

Thanks @TesteurManiak. Will merge after #1475.

[JaffaKetchup]

Hey @tlserver,
Unfortunately, #1475 has wreaked havoc on this PR. It appears as though many of the changes you made may have been fixed?
If you're still up to it, can you resolve the conflicts?
Apologies for the changes.

[tlserver]

Ok, but I am traveling right now. I will go back tomorrow.

[tlserver]

I try to resolve the conflicts.
1. CustomPoint<int> is not used in this plugin explicitly: change CustomPoint to always double to avoid potential error.

1. TileCoordinates extend CustomPoint<int> now, so remade CustomPoint. Now explicitly declare the return type in double, int or T.
2. Some property are num and some are double, but seem having no good reason: change to double for consistency.
3. mapState.nonrotatedSize and mapState.size is always available after widget initlized: change its getter to non-nullable.
4. CustomPoint.multiplyBy() have same functionality as operator *: make as deprecated. now removed for this PR is consider to be use for V4.

Significant changes since review

[JaffaKetchup]

Thanks @tlserver, we'll try to review this quickly.