[Feature request] highlight `iffalse` block as a comment about vscode-latex-basics

[jlelong]

Thanks for your report. I will investigate how to best support \iffalse/\fi.
A complete support would require to catch nested \ifXXXX/\fi and I am not sure how easily this can be achieved. The grammar is already very long and maintenance has become a main concern.

[ian-h-chamberlain]

Ah, interesting point about nesting and stuff, I hadn't considered that. I found this related issue which discusses some of the trade-offs and implementation: lervag/vimtex#1988
Given the complexity I think this is not as simple of a task as I initially thought 😅

Although that example is a vim syntax, I think the same idea applies — basically the \iffalse begin/end would include other conditionals in its body, for example the Rust syntax includes comments recursively to support nesting: https://github.com/microsoft/vscode/blob/main/extensions/rust/syntaxes/rust.tmLanguage.json#L295-L305

Does the grammar already include any \if / \fi special for beginning/ending blocks, or would that also need to be added for this?