make DdcFrontendServerBuilder use custom sdk build options

[schultek]

This makes DdcFrontendServerBuilder use the same build options as DevCompilerBuilder for specifying a custom sdk for building.

This is needed for Jaspr to run in "flutter compatibility mode", as added in #4299

As these options are only available during the build phase, the PersistentFrontendServer is modified to not start immediately when it's created in the resource, but only when the builder calls ensureStarted with the respective options.

@Markzipan

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Changelog Entry ❗

Package	Changed Files
package:build_web_compilers	builder_pkgs/build_web_compilers/bin/fes_manager.dart builder_pkgs/build_web_compilers/lib/builders.dart builder_pkgs/build_web_compilers/lib/src/build_frontend_server/frontend_server_driver.dart builder_pkgs/build_web_compilers/lib/src/build_modules/workers.dart builder_pkgs/build_web_compilers/lib/src/ddc_frontend_server_builder.dart

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[Markzipan]

I like the changes - thanks! However, I recently landed some somewhat large changes to a few of these objects (hopefully the last). I'll take a look after the merge.

[schultek]

I've rebased my changes to resolve the conflicts. However maybe this isn't the right apporach, I see that the PersistentFrontendServer is now connecting via socket to an existing instance, which when I understand it right is managed by webdev.

Is this related to the dwds logic that webdev (and Jaspr) have? Maybe Jaspr can then pass these options there and don't need to go throug build_web_compilers.

[Markzipan]

PersistentFrontendServer now has two running modes: one that connects to an existing FES instance (socket) and another that creates a local instance (same as before). I think the changes here are fine - though we should actually extend these build options to PersistentFrontendServer.start, FesManager.start, and related functions in fes_manager.dart.

[schultek]

@Markzipan How is the FesManager started? I see it's a script in bin/ but I don't find how it is executed.

[Markzipan]

@schultek It's started as an aot process by webdev - but this change hasn't landed yet. I'm fine with landing this - and I can add those build options to my change when it's out for review.

WIP here: dart-lang/webdev#2836