grpc: change existing dial/server options that set initial window size to not disable BDP estimation (#9078)

Fixes https://github.com/grpc/grpc-go/issues/7923

Specifically, this PR handles part two of the proposal:
https://github.com/grpc/grpc-go/issues/7923#issuecomment-2549600066

It also fixes existing tests that relied on BDP estimation being turned
OFF to use the `WithStaticXxx` and `StaticXxx` options, and adds new
tests that verify the behavior of all options in a e2e fashion.

RELEASE NOTES:
* grpc: Deprecate `WithInitialWindowSize` and `InitialWindowSize`. These
are replaced by `WithInitialStreamWindowSize` and
`InitialStreamWindowSize` respectively.
* grpc: Change behavior of existing options that set initial window size
on client and server to not disable BDP estimation.