Fix duplicate logging of MsalUiRequiredException (in-repo copy of #3910)

[Iarek Kovtunenko (iarekk)]

In-repo copy of #3910 by Armin Azar (@armin-azar), opened so the azure-pipelines app runs the PR pipeline natively (fork PRs don't trigger it, and the required check is enforced by an enterprise ruleset that admin merge can't bypass).

Original commits and authorship by Armin Azar (@armin-azar) are preserved unchanged. Once this merges, #3910 will be closed as landed via this branch.

Validated earlier on manually-queued ADO build 1663620 (succeeded).

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Original PR description (#3910):

Fix duplicate logging of MsalUiRequiredException

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Summary of the changes (Less than 80 chars)

Stop double-logging MsalUiRequiredException

Description

MsalUiRequiredException is already logged internally by MSAL.NET at error
level. Microsoft.Identity.Web additionally logged the same exception via
Logger.TokenAcquisitionError in two places in TokenAcquisition.cs, both
of which only rethrow/wrap the exception (no recovery logic depends on the
log call). This produced two log entries for a single MsalUiRequiredException,
as described in the issue.

This PR removes the redundant logging calls in those two catch blocks and
adds a comment explaining why nothing is logged there. All other
Logger.TokenAcquisitionError call sites (which handle exceptions MSAL does
not already log, e.g. certificate retry) are unchanged.

Added a unit test that reproduces the scenario from the issue (AcquireTokenSilent
called with no account/login hint, which MSAL throws MsalUiRequiredException for
synchronously) and asserts the log is not emitted.

Fixes #3528