[Maps] maps_legacy async bundle is loaded on startup

[flash1293]

Kibana version: 7.12 BC2

Describe the bug: On loading any page of Kibana, the async bundle of the maps_legacy bundle is loaded right away. It should only be loaded if it's actually required. It seems like all of the building blocks are in place, but an oversight placed it into the setup routine of the plugin (due to an interaction between region_map and tile_map)

Steps to reproduce:

1. Open Kibana home page
2. Observe /bundles/plugin/mapsLegacy/mapsLegacy.chunk.1.js being loaded

Expected behavior:
This bundle shouldn't be loaded.

Any additional context:
Path how it gets loaded in the setup phase:

kibana/src/plugins/maps_legacy/public/plugin.ts

Line 56 in 4584a8b

const getBaseMapsVis = () => new BaseMapsVisualizationProvider();

kibana/src/plugins/maps_legacy/public/map/base_maps_visualization.js

Line 33 in 4584a8b

this._mapIsLoaded = this._makeKibanaMap();

kibana/src/plugins/maps_legacy/public/map/base_maps_visualization.js

Line 92 in 4584a8b

const modules = await lazyLoadMapsLegacyModules();

kibana/src/plugins/maps_legacy/public/lazy_load_bundle/index.ts

Line 23 in 4584a8b

const { KibanaMap, L, ServiceSettings } = await import('./lazy');

triggered by

kibana/src/plugins/region_map/public/plugin.ts

Line 97 in 3b3327d

BaseMapsVisualization: mapsLegacy.getBaseMapsVis(),

[elasticmachine]

Pinging @elastic/kibana-gis (Team:Geo)

[thomasneirynck]

I can take a look at this. We need to remove the dependency from Vega from maps_legacy (#89304), so this could be part of that refactoring effort.

[thomasneirynck]

this was fixed by #92918 and #96093.

• [Maps] Isolate maps-setting froms maps_legacy #92918 isolated the dependencies in a new plugin (mapsEms)
• The chunk was due to a setup-dependency by the maps-licensing-plugin, which was removed by [Maps] Enable all zoom levels for all users #96093.