redesign package folders for DSM7 compatibility and use alternate TMPDIR for all packages

[hgy59]

Description

This is a redesign of the framework generated installers

1. define installer variables SYNOPKG_PKGVAR, SYNOPKG_PKGTMP and SYNOPKG_PKGHOME for DSM7 compatibility of DSM5 and DSM6 packages
2. create home and tmp folders for DSM7 compatibility of DSM5 and DSM6 packages
3. implement alternate TMPDIR for all packages and remove USE_ALTERNATE_TMPDIR variable (related to #5089)

§ 1. and 2. are based on the Package Filesystem, documented by synology (https://help.synology.com/developer-guide/integrate_dsm/fhs.html)

Checklist

• [ ] Build rule all-supported completed successfully
• [ ] New installation of package completed successfully
• [ ] Package upgrade completed successfully (Manually install the package again)
• [ ] Package functionality was tested
• [ ] Any needed documentation is updated/created

Type of change

• [ ] Bug fix
• [ ] New Package
• [ ] Package update
• [x] Includes small framework changes
• [x] This change requires a documentation update (e.g. Wiki)

[bakerboy448]

this would also fix https://github.com/SynoCommunity/spksrc/issues/5081

[Safihre]

@hgy59 Don't we still need this?