This could be done by each application, but it does cost only a few
lines of code, and it helps standardizing the Owl ecosystem.
For example, some library (such as o_spreadsheet) needs to mock side
effects, and Odoo also needs to do that, so this prevents duplicated effort.
closes#686
This rev. moves the logic of batching the notifications of changes
occurring in the same microtask tick, from the observer, to the
listeners (the context, and the render function of components).
By doing so in render, we ensure that similar renderings are
batched in a single one, wherever they come from (state change,
store change, direct call...).
Géry Debongnie