Replace PROCESS_ASSETS_STAGE_SUMMARIZE with PROCESS_ASSETS_STAGE_OPTIMIZE_SIZE

[phil-w]

As per issue #38, current use of this with the latest tools ( Webpack 5.65.0 and imagemin-web-webpack-plugin 3.3.6) throws a deprecation warning from Webpack:
BREAKING CHANGE: No more changes should happen to Compilation.assets after sealing the Compilation.
Do changes to assets earlier, e. g. in Compilation.hooks.processAssets.
Make sure to select an appropriate stage from Compilation.PROCESS_ASSETS_STAGE*._

Looking at plugin.js here, in "hookPlugin" there is the code as below (lines 111 etc).
So imagemin-web-webpack-plugin is using PROCESS_ASSETS_STAGE_SUMMARIZE... I guess they want something "earlier", and in any case like the earlier "PROCESS_ASSETS_STAGE_OPTIMIZE_SIZE " sounds like the right place.

I'll see if I can learn enough GitHub to do it myself, but otherwise, can that be done please?

if (compiler.hooks && compiler.hooks.thisCompilation && compiler.hooks.processAssets) {
        // webpack 5.x
        compiler.hooks.thisCompilation.tap('ImageminWebpWebpackPlugin', compilation => {
            compilation.hooks.processAssets.tapAsync({
                name: 'ImageminWebpWebpackPlugin',
                stage: compiler.webpack.Compilation.PROCESS_ASSETS_STAGE_SUMMARIZE
            }, (assets, cb) => onEmit(compilation, cb));
        })
    }

[Tofandel]

+1 for this, this is also how I had done it in an old fork for webpack 5 support

https://github.com/Tofandel/imagemin-webp-webpack-plugin/blob/master/plugin.js

Though you should use PROCESS_ASSETS_STAGE_OPTIMIZE