Fixes to String.Format

[edleno2]

Description

• Fixed lower case "g" to return exponential numbers like 1.23e+02 (note lower case 'e')
• Fixed F format for integers so it does not try to zero pad fractional part - integers don't have any fractional part
• Fixed one-off math issues in format N and calculation of significant digits
• Fixed format N rounding to allow that next character may be the decimal point and not the next significant digit

Motivation and Context

While adding unit tests for String.Format it was noted that there were either bugs in nanoFramework, or inconsistency with .Net Core 5. These changes bring all unit tests into compliance with .Net Core 5.

• Related Add explanation on supported numeric format strings supported Home#770

How Has This Been Tested?

Win32 unit tests run on both nanoFramework and .Net Core 5

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Unit Tests (work on Unit Tests, has no impact on code or features)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[nfbot]

@edleno2 there are issues with the code style on the source files.
A PR was submitted with the code style fixes. Please click https://github.com/edleno2/nf-interpreter/pull/8, review the changes if you want and merge it.

Make sure to follow the project code style. Check the details here on how it works and the tools required to help you with that.

[josesimoes]

LGTM!