[FEATURE] Use dynamic path for typo3temp/var/

All TYPO3 Core areas where typo3temp/var/ was directly used,
the new Environment::getVarPath() API is now used.

When running via composer or setting the environment
variable "TYPO3_PATH_APP", the folder is $projectRootPath . /var
otherwise "typo3temp/var/" as before.

Additional changes to the default naming scheme
- Cache folders are now named lower-case (Cache/Code becomes
cache/code). 
- Install tool session files are stored within "var/session" instead of
"var/InstallToolSessions".
- Extension Manager files are now within "var/extensionmanager"
in a lower-cased variant
- log files are now placed into "var/log" instead of "var/logs"
- lock files are now placed into "var/lock" instead of "var/locks"

Resolves: #84545
Releases: master
Change-Id: Ifa57413cd212243387532ffb3435cfca361a582b
Reviewed-on: https://review.typo3.org/56413


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>