Publicly accessible PrettyPrint in CheckResult #2582

[modery]

Currently there is no publicly accessible PrettyPrint function. The TexlParser.Format function does the right job, but it is only accessible internally. By providing a publicly accessible function, other tools can make use of it to format PowerFx code in a nicer way.
This contribution adds a publicly accessible PrettyPrint function, CheckResult.ApplyFormat(), as requested in #2582

Fix

File: ‎src/libraries/Microsoft.PowerFx.Core/Public/CheckResult.cs
CheckResult.cs has been updated with a new function called ApplyFormat(), which returns the pretty-printed form of the expression. This way, we can use an Engine() object with CheckResult, set the text, and apply formatting:

var check = new CheckResult(new Engine(new PowerFxConfig()));
check.SetText(script);
var formatted = check.ApplyFormat();

Tests

File: ‎src/tests/Microsoft.PowerFx.Core.Tests.Shared/FormatterTests.cs
Test cases have been added similar to the existing TestPrettyPrint test case