Extract shape text from drawio XML for searching

MarkdownHelper.escapeDiagramSpec(). Parse using mxgraph api, need to add/verify support for decompression - both compressed and uncompressed diagrams shall be supported.

Origin	common/engineering/engineering.yml 22:5
Uri	engineering://nasdanika/modules/core/modules/common/issues/drawio-escaping
Categories	Good First Issue
Target	Common
Workable