Most LSPs will complete case-insensitive matches, particularly from
lowercase to uppercase.  In some cases, notably Pyright, this is given
as a simple insert text instead of TextEdit.  When this happens, the
prefix text was left unedited.

This commit adds new functions to `Transaction` that allow creating
edits that might potentially overlap. Any change that overlaps
previous changes is ignored. Furthermore, a utility method is added
that also drops selections associated with dropped changes (for
transactions that are created from a selection).

This is needed to avoid crashes when applying multicursor
autocompletions, as the edit from a previous cursor may overlap
with the next cursor/edit.

Multicursor completions may overlap and therefore overlapping
completions must be dropped to avoid crashes. Furthermore, multicursor
edits might simply be out of range if the word before/after the cursor
is shorter. This currently leads to crashes, instead these selections
are now also removed for completions.

This commit also significantly refactors snippet transaction generation
so that tabstops behave correctly with the above rules. Furthermore,
snippet tabstops need to be carefully mapped to ensure their position
is correct and consistent with our selection semantics. Finally,
we now keep a partially updated Rope while creating snippet
transactions so that we can fill information into snippets that
depends on the position in the document.

… scope (#6242)

* misc: missing inline, outdated link

* doc: Add new theme keys and config option to book

* fix: don't panic in Tree::try_get(view_id)

Necessary for later, where we could be receiving an LSP response
for a closed window, in which case we don't want to crash while
checking for its existence

* fix: reset idle timer on all mouse events

* refacto: Introduce Overlay::new and InlineAnnotation::new

* refacto: extract make_job_callback from Context::callback

* feat: add LSP display_inlay_hint option to config

* feat: communicate inlay hints support capabilities of helix to LSP server

* feat: Add function to request range of inlay hint from LSP

* feat: Save inlay hints in document, per view

* feat: Update inlay hints on document changes

* feat: Compute inlay hints on idle timeout

* nit: Add todo's about inlay hints for later

* fix: compute text annotations for current view in view.rs, not document.rs

* doc: Improve Document::text_annotations() description

* nit: getters don't use 'get_' in front

* fix: Drop inlay hints annotations on config refresh if necessary

* fix: padding theming for LSP inlay hints

* fix: tracking of outdated inlay hints should not be dependant on document revision (because of undos and such)

* fix: follow LSP spec and don't highlight padding as virtual text

* config: add some LSP inlay hint configs

fixes #6235

The current test DSL currently has no way to express being at the end of
a line, save for putting an explicit LF or CRLF inside the `#[|]#`. The
problem with this approach is that it can add unintended extra new lines
if used in conjunction with raw strings, which insert newlines for you.

This is a simple attempt to mitigate this problem. If there is an
explicit newline character at the end of the selection, and then it
is immediately followed by the same newline character at the right end
of the selection, this following newline is removed. This way, one can
express a cursor at the end of a line explicitly.

test::plain uses char indices when it should use byte indices