Update Resource preview to support settings tag in Weblinks

[smg6511]

What changed and why

Added condition in getPreviewUrl to take system settings (including ones created by Extras like ClientConfig) into account and parse them before checking validity. Previously, Weblinks with valid targets (Resource or static URLs) supplied by a setting tag would cause preview to fail and an error message to be logged.

How to test

1. Create a system setting and store either the ID of an existing, viewable Resource or a static URL.
2. Use this setting as the content value in a new Weblink.
3. Verify that the "View" button (as well as context menu item in the tree) is active and leads to the expected Resource or website.

Related issue(s)/PR(s)

This PR addresses the issue raised in the MODX Community forum by @SnowCreative.

Compatibility notes

n/a

Breaking change assessment

n/a

Test coverage

No pre-existing tests for this method; none currently planned.

Contributors

See related issues above.

AI tool use

n/a

[codecov]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 21.67%. Comparing base (5a484de) to head (3c5699b).
⚠️ Report is 12 commits behind head on 3.x.

Files with missing lines	Patch %	Lines
core/src/Revolution/modResource.php	0.00%	14 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.x   #16954      +/-   ##
============================================
- Coverage     21.67%   21.67%   -0.01%     
- Complexity    10786    10791       +5     
============================================
  Files           566      566              
  Lines         33149    33170      +21     
============================================
+ Hits           7186     7189       +3     
- Misses        25963    25981      +18     

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