chore: Un-revert enabling CSP by default

[kgabryje]

SUMMARY

This PR fixes a regression in #24262 that required reverting it (#24476). If TALISMAN_ENABLED is false, the csp_nonce function is undefined - here I introduced a macro that checks if the function is defined before calling it.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #24543 (2223050) into master (66f59e5) will increase coverage by 0.10%.
The diff coverage is 100.00%.

❗ Current head 2223050 differs from pull request most recent head a2aed5e. Consider uploading reports for the commit a2aed5e to get more accurate results

@@            Coverage Diff             @@
##           master   #24543      +/-   ##
==========================================
+ Coverage   68.98%   69.08%   +0.10%     
==========================================
  Files        1906     1906              
  Lines       74114    74114              
  Branches     8155     8155              
==========================================
+ Hits        51124    51200      +76     
+ Misses      20871    20795      -76     
  Partials     2119     2119              

Flag	Coverage Δ
hive	53.92% <100.00%> (?)
javascript	55.78% <ø> (-0.01%)	⬇️
mysql	79.40% <100.00%> (?)
postgres	79.48% <100.00%> (-0.01%)	⬇️
presto	53.82% <100.00%> (-0.01%)	⬇️
python	83.48% <100.00%> (+0.21%)	⬆️
sqlite	78.04% <100.00%> (-0.01%)	⬇️
unit	54.69% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../superset-ui-core/src/models/ExtensibleFunction.ts	100.00% <ø> (ø)
superset/config.py	92.00% <100.00%> (+0.02%)	⬆️
superset/initialization/__init__.py	91.04% <100.00%> (-0.31%)	⬇️

... and 8 files with indirect coverage changes

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