trunk_staging: set codename to Baklava

Set RELEASE_PLATFORM_VERSION_CODENAME and related build flags to
Baklava.

Commit generated by running the following commands:

    $ build-flag --quiet --release=trunk_staging set RELEASE_PLATFORM_VERSION_CODENAME Baklava
    $ build-flag --quiet --release=trunk_staging set RELEASE_PLATFORM_VERSION_ALL_CODENAMES Baklava
    $ build-flag --quiet --release=trunk_staging set RELEASE_PLATFORM_VERSION_ALL_PREVIEW_CODENAMES Baklava
    $ build-flag --quiet --release=trunk_staging set RELEASE_PLATFORM_VERSION_KNOWN_CODENAMES Base,Base11,Cupcake,Donut,Eclair,Eclair01,EclairMr1,Froyo,Gingerbread,GingerbreadMr1,Honeycomb,HoneycombMr1,HoneycombMr2,IceCreamSandwich,IceCreamSandwichMr1,JellyBean,JellyBeanMr1,JellyBeanMr2,Kitkat,KitkatWatch,Lollipop,LollipopMr1,M,N,NMr1,O,OMr1,P,Q,R,S,Sv2,Tiramisu,UpsideDownCake,VanillaIceCream,Baklava

Bug: 354023031
Test: build-flag --quiet --all-releases get RELEASE_PLATFORM_VERSION_CODENAME
Test: build-flag --quiet --all-releases get RELEASE_PLATFORM_VERSION_ALL_CODENAMES
Test: build-flag --quiet --all-releases get RELEASE_PLATFORM_VERSION_ALL_PREVIEW_CODENAMES
Test: build-flag --quiet --all-releases get RELEASE_PLATFORM_VERSION_KNOWN_CODENAMES
Ignore-AOSP-First: unblock work to set codename to Baklava (this CL can be CP'd to AOSP afterwards)
Change-Id: I5451eb5122d266400ccf119cf91806e69d65a503