[xDS] change client-side HTTP filters to use the new config mechanism

[markdroth]

Built on #40938.

Change the client-side xDS HTTP filters to use the new filter config mechanism introduced in #40938.

[markdroth]

I've split this PR into 3 parts:

• [filter stack] mechanism for passing configs to filters at construction time #40929: adds a mechanism to pass a filter config at filter chain construction time
• [xDS] change ConfigSelector to use a separate filter chain for each route #40938: changes the ConfigSelector to return a filter chain for each RPC, so we have a separate filter chain for each route
• this PR: what's left here is just changing the client-side xDS HTTP filters to use the new config mechanism

For now, I'm putting this PR back into draft state, since github doesn't support diffbase. Once the preceding PRs are merged, I'll merge master into this PR and mark it ready for review.

[markdroth]

Closing this in favor of #40938.