auro-docsite: WCSS 4.3.0 will not build

[blackfalcon]

Describe the bug

When building the site with the new WCSS update, there is the following error

Creating an optimized production build...
Failed to compile.

./src/sass/index.scss
SassError: argument `$string` of `str-slice($string, $start-at, $end-at:-1)` must be a string
        on line 16 of node_modules/@aurodesignsystem/webcorestylesheets/dist/utilityFunctions/_capitalize.scss, in function `str-slice`
        from line 16 of node_modules/@aurodesignsystem/webcorestylesheets/dist/utilityFunctions/_capitalize.scss, in function `auro_capitalize`
        from line 88 of node_modules/@aurodesignsystem/webcorestylesheets/dist/utilityMixins/_spacingUtility.scss, in mixin `auro-spacing`
        from line 98 of node_modules/@aurodesignsystem/webcorestylesheets/dist/utilityMixins/_spacingUtility.scss
        from line 33 of src/sass/index.scss
>>   @return to-upper-case(str-slice($string, 1, 1)) + str-slice($string, 2);

   ------------------------^

To Reproduce

Steps to reproduce the behavior:

1. Go to 'https://itsals.visualstudio.com/E_SharedServices_Platform/_build/results?buildId=2081745&view=logs&j=3dc8fd7e-4368-5a92-293e-d53cefc8c4b3&t=5cfe65a4-d7cb-5934-e953-1c67617821f4&l=46'

Expected behavior

Site will build

Exit criteria

This issue will be resolved once the docsite is able to build with the latest version of WCSS.

[marnel-mangrubang]

We found that this issue is caused by the changes made in the latest release v4.3.0. Changes that were made in the _spacing-options.scss of the WebCoreStyleSheets repo, more specifically, the addition of numbers to the existing $auro-spacing-options variable.
https://github.com/AlaskaAirlines/WebCoreStyleSheets/pull/145/files

With the changes, the utility function called auro_capitalize is now failing because it the function expects the arguments to always be of string type.

We believe that adding a type check in the auro_capitalize function inside the WebCoreStyleSheets repo, will resolve the build errors happening in the AuroDocsSite when trying to run a build.

[blackfalcon]

See companion issue to be resolved

• WCSS will not build in auro docsite WebCoreStyleSheets#148