Fix site scoped contextinfo

[jorisvanduyse]

What & why

This fixes SharePoint request-digest acquisition for site-scoped SharePoint URLs.

SharePoint Uri Builder.GetHost() intentionally returns only the hostname, but request-digest calls used it for /_api/contextinfo. For URLs such as https://tenant.sharepoint.com/sites/site, this caused the request to target the tenant root instead of the configured site.

The change adds a site-base URL accessor and uses it for request-digest acquisition in CreateList, both CreateListItem overloads, CreateFolder, and UpdateListItemMetaDataField. GetHost() remains unchanged for callers that require hostname-only behavior.

Regression tests verify that contextinfo requests retain the configured /sites/<site> path.

Linked work

Fixes #8932

How I validated this

• I read the full diff and it contains only changes I intended.
• I built the affected app(s) locally with zero compilation errors.
• I ran the change in Business Central and confirmed it behaves as expected.
• I added or updated tests for the new behavior, or explained below why none are needed.

What I tested and the outcome

• Built the affected System Application and test applications locally with zero compilation errors.
• Published a temporary System Application build to a disposable local BC29 container using normal synchronization and upgrade semantics.
• Ran the SharePoint Client Test codeunit (132970) manually in the BC Test Tool.
• Confirmed the regression before the fix:
  • Expected: site-scoped .../sites/<site>/_api/contextinfo/
  • Actual: tenant-root .../_api/contextinfo/
• Published the fixed System Application and reran the same tests.
• Confirmed that TestCreateFolder, TestCreateListRequestDigestUsesSiteScopedUrl, and TestCreateListItemRequestDigestUsesSiteScopedUrl pass with the fix applied.
• Also verified the original scoped SharePoint scenario manually in a disposable v28.1 container.

Risk & compatibility

This is an internal URI-construction change with no schema, data-upgrade, permission, or public API contract changes.

GetHost() is unchanged. The new site-base URL accessor is used only for request-digest acquisition, ensuring existing hostname-only consumers retain their behavior.
Fixes #8932 is the GitHub issue link. GitHub will automatically link it, and close the issue when the PR is merged.

[jorisvanduyse]

@microsoft-github-policy-service agree