Treat ] before dot like ) in QuickParse completion

[T-Gro]

Fixes #4966

a.[0].Data., a[0].Data., [1;2].Length. now trigger expression-typings
instead of incorrectly feeding Data/Length back as qualifying idents.

[github-actions]

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

[T-Gro]

Review: Approve ✅

Clean, minimal fix with good test coverage.

Code change: The one-line addition || lineStr[pos - 1] = ']' is the correct analog of the existing ')' check. When the character before a trigger-dot is ] (closing an indexer expression), the token sequence is an expression tail, not part of a qualifying long-ident. The throwAwayNext = true discard logic is exactly what's needed.

Tests: Good theory-based coverage — positive cases for ] (legacy explicit-dot, modern indexer, list literal, nested), regression guard for existing ) handling, and negative cases verifying plain long identifiers aren't over-discarded.

Minor suggestion (non-blocking): The comment on lines 411–414 could mention the ] case alongside someCall(args).Name (e.g. add a.[0].Data.Name) to match the now-broader condition, but this is cosmetic.

Release notes: Well-phrased with correct issue/PR links.