fastbootd: Add commands for logical partitions.

This patch adds the following new commands to fastbootd:

    getvar is_logical:<partition>
    create-logical-logical-partition <partition> <size>
    delete-logical-partition <partition>
    resize-logicallogical-partition <partition> <size>

All of these commands operate on logical partitions only, and require a
properly configured "super" partition to operate.

Bug: 78793464
Test: fastboot create-logical-partition example 4096
      fastboot create-logical-partition example 4096 returns error
      fastboot getvar is-logical:example returns "yes"
      fastboot getvar partition-size:example returns "1000"
      fastboot resize-logicalpartition example 8000
      fastboot getvar partition-size:example returns "2000"
      fastboot delete-logical-partition example
      fastboot getvar is-logical:example returns error
      fastboot getvar is-logical:system_a returns "no"

Change-Id: Iff323eabcf5c559fa04c7c92574650b01803eb1f