Snippet optional transforms are not applied correctly when reusing the same variable

[dogoku]

• VSCode Version: Insiders v1.18.0 (86e057c)
• OS Version: N/A

Related to #36089, transforms are working for optional matches, however, when reusing the same variable (e.g. $1) only the first transform is applied.

Given the following simplified example:

//TM_FILENAME_BASE: `my-awesome-module`
[
"function ${1:${TM_FILENAME_BASE/^(.)|-(.)/${1:/upcase}${2:/upcase}/g}} () {}",
"module.exports = $1;" //<<<< BROKEN
]

//Expected
function MyAwesomeModule () {}
module.exports = MyAwesomeModule;

//Actual
function MyAwesomeModule () {}
module.exports = My-awesome-module;

In case you missed it, the second use of $1 was not transformed properly, having only the first transform applied to it ${1:/upcase}, where as the second transform ${2:/upcase} was not applied at all, resulting in the string My-awesome-module instead of MyAwesomeModule

This is not the case for normal transforms (non-optional), e.g:

//TM_FILENAME_BASE: `myfile`
[
//Upcase the first 2 letters
"function ${1:${TM_FILENAME_BASE/^(.)(.)/${1:/upcase}${2:/upcase}/g}} () {}",
"module.exports = $1;"
]

//Result:
function MYfile () {}
module.exports = MYfile;