Add Replace function to UText

[alecxvs]

Scenario: The format bounds exist before the text selection

• Solution: Unaffected

Scenario: The format bound(s) exist after the text selection

• Solution: Move the bound to include the whole of the new phrase

Scenario: The format bound(s) exist within the text selection

• Sub-scenario A: The new phrase is shorter, and the format bound if unmoved no longer intersects the phrase
  • Solution: Move the format bound to the end of the phrase
• Sub-scenario B: The new phrase is the same length, larger, or is smaller but does not cut off any format bounds
  • Solution: Do not move the format bound
• Sub-scenario C: The new phrase is shorter and both beginning and end bounds of the format are outside the new phrase length
  • Solution: Remove the format, it no longer has applicable contents