Add support for variables in text style.

[GiniAppsPartners]

Brief Summary of Changes

Add support for variables in text style.

What does this PR address?

• GitHub issue (Add reference - #XX)
• Refactoring
• New feature
• Bug fix
• Adds more tests

Are tests included?

• Yes
• No

Reviewer, please note:

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I ran the full test suite before pushing the changes and all the tests pass.

[adimiz1]

You added the ability to add text style via String, but what about adding it via expression?
You can see the implementation in the Java PR
Also I've added a new expression myself to the iOS SDK, you can see it in the branch:
feature/angle_expression

[adimiz1]

Hi Alex
Please break this PR into two separate PR's
One for text style
And the other for expression normalization
Also please fix an comment I remarked on the expression normalization

[adimiz1]

A specific use case of regex expression should not impact the asString() function
This should be handled in the Regex expression and not outside of it

[GiniAppsPartners]

I understood that this is the new requirements (according to Patriks tests)
Meaning if the value contains "allSpaceAndOrDash" then asString() should return "_" otherwise the tests fail.