Ensures that text style properties are copied by value, not by reference (#4385) ...

* Ensures that text style properties are copied by value, not by reference
Fixes an issue where

* removed duplicate code

* Reduce loop over object properties to within deepCopyProperties

Measure Text API, expanded (#3921) ...

* Added TextStyle.measure function (Applies to https://github.com/pixijs/pixi.js/issues/3903).

* Moved measure function from TextStyle to Text and made static.

* Updated JSDocs.

* Updated JSDocs again.

* Updates based on suggestions by @bigtimebuddy in PR.

* Created PIXI.MeasuredText to capture all the information for measuring text.

* Fixes for ESLint

* Fixes for ESLint

* Added PIXI prefix to returning MeasuredText.

* Added import for MeasuredText in Text.js.

* Refactored MeasuredText to TextMetrics and moved `measure` function into it.

* Forgot to move Text.wordWrap to TextMetrics.wordWrap

* Further cleanup of TextMetrics.

* Fixes suggested by @bigtimebuddy

* Removed clone and equals from TextMetrics as they are unnecessary.

* Destructured references to TextMetrics instance in Text and privatized TextMetrics.wordWrap.

* Deprecates calculateFontProperties & getFontStyle

* Moved getFontStyle to TextMetrics

* Made toFontString method on TextStyle

* Cache calls made to context.measureText for individual characters

* Use a smaller (10x10) canvas for TextMetrics

Text style fixes (#3405) ...

* Correct reference to default style

* Unit tests for Text Style