Add Share component override and vartheme_social icon pack

Problem/Motivation

Varbase needs a themed Share component and a matching set of social icons so visitors can share content in a way that fits the design.

Proposed resolution

Add a Share component override and the vartheme_social icon pack.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ✅ Code review from 1 Varbase core team member
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes
• ✅ Release varbase-11.0.0-alpha3, varbase_starter-1.0.0-alpha2, vartheme_bs5-5.0.0-alpha3

Varbase update type

• ✅ No Update
• ➖ Optional Update
• ➖ Forced Update
• ➖ Forced Update if Unchanged

User interface changes

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• feat: #3591793 Add Share component override and vartheme_social icon pack