fix: keep tree view severity filters in sync with settings page

[andrewrobinsonhodges-snyk]

Description

Plumbing to allow the settings page to reflect changes in the severity filters made in the HTML tree view.

Needs the LS changes from snyk/snyk-ls#1316

Checklist

• Read and understood the Code of Conduct and Contributing Guidelines.
• Tests added and all succeed
• Linted
• CHANGELOG.md updated
• README.md updated, if user-facing

Screenshots / GIFs

Visuals that may help the reviewer. Please add screenshots for any UI change. GIFs are most welcome!

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

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[snyk-pr-review-bot]

PR Reviewer Guide 🔍

🧪 PR contains tests

🔒 No security concerns identified

⚡ No major issues detected

📚 Repository Context Analyzed This review considered 22 relevant code sections from 13 files (average relevance: 0.63) docs/configuration-gaf-ls-ide-flow.md (lines 94-110) src/snyk/snykCode/views/suggestion/codeSuggestionWebviewScriptLS.ts (lines 1-244) package.json (lines 124-282) src/snyk/common/views/workspaceConfiguration/services/configurationPersistenceService.ts (lines 1-176) src/snyk/common/views/issueTreeProvider.ts (lines 1-23) src/snyk/common/languageServer/types.ts (lines 1-222) src/snyk/common/constants/languageServer.ts (lines 1-22) ... and 6 more file(s)