[vscode] Support keepWhitespace in SnippetTextEdit and insertSnippet

[rschnekenbu]

What it does

This introduces the support of the keepWhitespace optional value added in the TextEditor.insertSnippet API and SnippetTextEdit.

fixes #15131

How to test

1. install the following exension in the browser or electron example:

• src: snippet-sample-0.0.1-src.zip
• zip vsix: snippet-sample-0.0.1.zip

2. in a text file, insert text edits using the 3 following commands from the command palette on lines with different indentations:

• "Insert Snippet - keepWhitespace True",
• "Insert Snippet - keepWhitespace False"
• "Insert Snippet - keepWhitespace Undefined".
  These 3 commands will add 2 lines of text with 2 spaces at the beginning of each line. The keep whitespace parameter keeps or not the indentation at the beginning of the line. If you insert the text on an already indented line, 4 in video example, the insert with keepwhitespace parameter being true or false will behave differently. The second line will have a different indentation based on the parameter. If keepWhitespace is true, the second line will only have the spaces has defined in the snippet (2 in the extension case). If false or undefined, it will have snippet indentation (2) + current line indentation (4 in the video example) . The behavior is similar with the one on vscode.

Note: this only tests the insertSnippet() parameter addition.
The SnippetTextEdit keepWhiteSpace property is simply passed from the extension to the main, and transformed directly to equivalent monaco type.
When looking at

theia/packages/plugin-ext/src/main/browser/languages-main.ts

Line 1415 in 5e851cd

export function toMonacoWorkspaceEdit(data: WorkspaceEditDto | undefined): monaco.languages.WorkspaceEdit {

, in the case of a WorkspaceTextEditDto, the returned Monaco type IWorkspaceTextEdit also supports this keepWhitespace parameter.

Sample video:

2025-03-12.16-31-53.mp4

Follow-ups

None

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Contributed on behalf of STMicroelectronics

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

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