Improves the failure messages for the `template-var-assignment` schematic. After manual
testing of the schematic it's not quite clear for developers what the failure message means
without any context. The schematic now also references a short markdown file mentioning
what needs to be changed, but eventually this document needs to be expanded with more
information and context of the reasoning behind this change within Ivy.
PR Close#29708
Introduces a new update schematic called "template-var-assignment"
that is responsible for analyzing template files in order to warn
developers if template variables are assigned to values.
The schematic also comes with a driver for `tslint` so that the
check can be used wtihin Google.
PR Close#29608
Paul Gschwendtner