Poor performance of oelint.vars.mispell on larger files

[priv-kweihmann]

When scanning e.g. https://git.yoctoproject.org/poky/tree/meta/recipes-kernel/linux/linux-yocto-rt_6.6.bb (with the huge cve-exclusion_6.6.inc file), GetItemsFor takes ages for anything.
This seems to have been introduced with 2.13 release of oelint-parser