issue #7783: speed up explorer filter and large project tree open

[mattcasters]

Summary

Fixes #7783: the File Explorer filter became unusable with a few hundred–thousand files (multi-second freezes per keystroke). The same tree rebuild path also made opening a large flat project root expensive.

Two related problems were fixed:

1. Filter keystrokes (original issue)

• Debounce filter apply (~250 ms; Enter applies immediately)
• In-memory ExplorerTreeModel: one full VFS walk, then subsequent filter keystrokes match/render from memory only
• Filter rebuilds do not call IExplorerRefreshListener.beforeRefresh() (no git status per character)
• Removed recursive hasMatchingDescendant VFS probes (the O(n×depth) double-walk)
• Explorer filter uses non-fuzzy SearchMatcher (substring/word only)

2. Project open / tree paint cost (same root causes)

• HopFileTypeBase.isHandledBy: extension match is pure string — no HopVfs.getFileObject per plugin per file
• Extension/basename maps in ExplorerPerspective for O(1) type resolution; folders take FolderFileType via known isFolder flag
• FolderFileType / GenericFileType: no VFS isFolder/isFile probes during type resolution
• Same string-extension approach for Archive, Excel, Parquet, NoExtension types
• Single-pass folder listing (classify once, then sort folders/files)
• Git paint path normalization without VFS (when git plugin is enabled)

Measured on a ~10k-file project root (git disabled): open dropped from ~10s to ~6s (~40%). Filter typing is interactive after the first index build.

Reviewer notes

Please focus review on these areas:

1. ExplorerPerspective filter path

   • scheduleFilterApply / applyPendingFilter / applyFilterFromModel / ensureFullTreeModel
   • Confirm F5 still refreshes git status while filtering, but normal keystrokes do not
   • Confirm clearing the filter restores expand state via saveTreeState / restoreTreeState
   • Index invalidation: treeModel.clear() on structural refresh(), show-hidden, create/delete/rename (via refresh())

2. getFileType(path, isFolder) + indexFileTypes()

   • First matching extension wins (plugin order). Flag any type that used non-extension logic that no longer maps cleanly
   • FolderFileType.isHandledBy now always returns false — callers must pass isFolder=true or select the type explicitly. Search for other callers if concerned
   • GenericFileType is the catch-all for unmatched files without VFS

3. HopFileTypeBase.extractExtension / extractBaseName

   • Hidden files like .gitignore intentionally have no “extension”
   • Compound filters (*.xls;*.xlsx) are split on ;

4. Git GitGuiPlugin.getAbsoluteFilename

   • Keys must stay consistent between refreshChangedFiles and filePainted (both use the same string normalizer now)
   • Worth a quick smoke test: git project with staged/modified files still get color in the explorer

5. Out of scope / known remaining cost

   • Creating many SWT TreeItems for a flat 10k root is still inherently heavy; this PR does not virtualize the tree
   • First filter after open may still walk the full tree once to fill the index (by design)

Test plan

• Unit: HopFileTypeBaseTest, ExplorerTreeModelTest
• Manual: project with ~1k+ files — type in explorer filter; characters should not freeze UI; matches under nested folders appear after debounce
• Manual: clear filter — previous expand/collapse state restored
• Manual: F5 while filtering — tree updates and git colors (if git enabled) refresh
• Manual: open large flat project — tree populates without multi-10s freezes
• Manual: open pipeline/workflow/text files from explorer still uses correct handlers/icons
• Manual (git): modified/staged/ignored files still colored after explorer refresh

Fixes #7783