Standardize convention for `-common` modules

[trask]

Currently, -common modules have inconsistent naming patterns:

With library dependency:

• rxjava-3-common
• ktor-2-common
• graphql-java-common
• servlet-javax-common

Without library dependency:

• lettuce-common
• netty-common
• servlet-common
• ktor-common

Proposed Convention

• <library>-common = Pure utility/abstraction code with NO library version dependency
• <library>-common-<major.minor> = Shared code requiring minimum library version
• <library>-common-<variant> = Special case for javax

Required Changes

Current Module	New Module
rxjava-3-common	rxjava-common-3.0
ktor-2-common	ktor-common-2.0
graphql-java-common	graphql-java-common-12.0
servlet-javax-common	servlet-common-javax

[self-sasi]

Hey @trask, can I work on this?