Move hit test position inside text container to get correct cursor position

[leonspok]

The problem was that by default if you press in the inset area of UITextView cursor is positioned at the beginning of UITextView.

UITextView has these methods available for overriding:

/* Hit testing. */
- (nullable UITextPosition *)closestPositionToPoint:(CGPoint)point;
- (nullable UITextPosition *)closestPositionToPoint:(CGPoint)point withinRange:(UITextRange *)range;
- (nullable UITextRange *)characterRangeAtPoint:(CGPoint)point;

They are used to determine cursor position when user presses on UITextView. We can move the given point to the closest point inside UITextView's text content, which enables it to return proper cursor position.

Here is an example:

Green - fixed version, red - default behaviour.

[codecov-io]

Codecov Report

Merging #595 into master will decrease coverage by 0.38%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #595      +/-   ##
==========================================
- Coverage   58.07%   57.68%   -0.39%     
==========================================
  Files          90       90              
  Lines        3859     3885      +26     
==========================================
  Hits         2241     2241              
- Misses       1618     1644      +26

Impacted Files	Coverage Δ
...ttoAdditions/Source/Input/ExpandableTextView.swift	52.51% <0%> (-12.09%)	⬇️

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