feat(agent): add experimental option: scope of indentation filter.

[icycodes]

Complete TAB-268

Add this config to enable experimental feature:

[postprocess.limitScopeByIndentation]
keepBlockScopeWhenCompletingLine = true

When completion is continuing the current line, limit the scope to:

• false(default): the line scope, meaning use the next indent level as the limit.
• true: the block scope, meaning use the current indent level as the limit.

Example:
off:

on:

[wsxiaoys]

Please add experimental prefix