refactor(map): report the GL viewport from a module of its own

reportGlViewport says what a GL map shows, its bounds and its zoom on the
raster tile scale, and has its own test for that scale. MapViewGL only
wires it to moveend and idle, and its test checks that wiring. The GL map
tests put the zoom back to its default before each test, as they do for
every other value a test overrides, instead of each test restoring it.

client/src/components/Map/MapViewGL.test.tsx

@@ -257,6 +257,7 @@ beforeEach(() => {
   glMap.querySourceFeatures.mockReturnValue([])
   glMap.getCanvas.mockImplementation(() => document.createElement('canvas'))
   glMap.getBearing.mockReturnValue(0)
+  glMap.getZoom.mockReturnValue(10)
   glMap.queryTerrainElevation.mockReturnValue(null)
   // A busy style, a refused source and a custom layer list are each set by one test
   // for the case it covers. Put back here, or every test after it would silently run
@@ -1575,7 +1576,6 @@ describe('MapViewGL', () => {
     const list = calls[calls.length - 1][0]
     act(() => { list.querySelectorAll('button')[1].click() })
     expect(onPoiClick).toHaveBeenCalledWith(other)
-    vi.mocked(glMap.getZoom).mockReturnValue(10)
   })
 
   const pinGlyph = (Icon: LucideIcon) => renderIconMarkup(React.createElement(Icon, { size: 13, color: 'white', strokeWidth: 2.5 }))
@@ -2215,14 +2215,12 @@ describe('MapViewGL', () => {
     expect((window as any).__trek_map).toBeUndefined()
   })
 
-  it('FE-COMP-MAPVIEWGL-059: pan and zoom report the visible bbox for the POI explore pill, with the zoom on the raster tile scale', async () => {
+  it('FE-COMP-MAPVIEWGL-059: pan and zoom report the visible bbox and tile zoom for the POI explore pill', async () => {
     const onViewportChange = vi.fn()
-    vi.mocked(glMap.getZoom).mockReturnValue(10)
     render(<MapViewGL places={[]} fitKey={1} onViewportChange={onViewportChange} />)
     await act(async () => {})
 
     act(() => { mapHandler('moveend')() })
-    // The GL engine counts on 512 px tiles; a raster tile's zoom is one step further in.
     expect(onViewportChange).toHaveBeenCalledWith({ south: 0, west: 0, north: 1, east: 1 }, 11)
   })