chore: bump superset to 0.18.6

[villebro]

SUMMARY

Pull in the following PRs from superset-ui:

• refactor(core): move mexp from plugins to core apache-superset/superset-ui#1371
• fix: Pivot table now at 100% width apache-superset/superset-ui#1360
• chore(plugin-chart-echarts): bump to ECharts 5.2.1 apache-superset/superset-ui#1370
• refactor: improve code smell for postprocessing apache-superset/superset-ui#1368

This PR also removes the direct dependency on math-expression-evaluator, as it's now a dependency in superset-ui/core that exposes the relevant functionality along with full test coverage.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

1. Create a formula annotation using both NVD3 and ECharts timeseries charts
2. Notice that formulas render like before

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 #16807 (f8278d2) into master (997320a) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #16807      +/-   ##
==========================================
- Coverage   76.89%   76.89%   -0.01%     
==========================================
  Files        1005     1005              
  Lines       54169    54163       -6     
  Branches     7456     7454       -2     
==========================================
- Hits        41653    41648       -5     
+ Misses      12272    12271       -1     
  Partials      244      244              

Flag	Coverage Δ
javascript	71.08% <100.00%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
...ontrols/AnnotationLayerControl/AnnotationLayer.jsx	83.85% <100.00%> (+0.01%)	⬆️

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[zhaoyongjie]

LGTM