Add GetCharacterBoundingRectangle API.

Add GetCharacterBoundingRectangle API.

Calculate the character size and position:
- X, the left starting point of the character.
- Y, the left top point of the character.
- Width.
- Height.

Function prototype: GetCharacterBoundingRectangle(ModelPtr model, uint32_t charIndex);

Add new API to TextGeometry.

Reference patches:
https://review.tizen.org/gerrit/c/platform/core/uifw/dali-toolkit/+/266891

Change-Id: Ifcdcca5ae3af52da79af899b26d3a273713e012d