This patch is the first step in the realization of T5382 and T4760.
This patch sets the minimum required version of KF5 to 5.49 and requires KSyntaxHighlighting. The higher version is required because of the extensions in KSyntaxHighlighting done in D14434 which we need for this move.
The transition to KSyntaxHighlighting is done for Maxima first. Other systems will be migrated step by step soon.