Reduce public visibility of some SVM related structs and APIs #16048

Job	Run time
check	2m 29s
cargo-test-sbf (token/program)	6m 26s
test (token/cli, token/program, token/program-2022, associated-token-account/program, instruction...	17m 45s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	12m 27s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	7m 37s
test (single-pool/cli, single-pool/program)	14m 42s
cargo-test-sbf (token-upgrade/program)	7m 50s
test (token-upgrade/cli, token-upgrade/program)	13m 22s
cargo-test-sbf (feature-proposal/program)	6m 17s
cargo-test-sbf (governance/addin-mock/program, governance/program)	9m 33s
cargo-test-sbf (name-service/program)	6m 32s
cargo-test-sbf (stake-pool/program)	9m 0s
cargo-test-sbf (single-pool/program)	7m 57s
	2h 1m 57s

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