Add offline/online-sdk-docs in Soong.

Since support libraries have been migrated to Soong, these docs modules
currently are ready to be supported in Soong.

Bug: b/70351683
Test: m -j offline-sdk-docs
Change-Id: I8739d94909c7cc830c30fa3d1047d26761cc5076
Merged-In: I8739d94909c7cc830c30fa3d1047d26761cc5076