Ellipsize (#467)

* feat: add Ellipsize enum

* chore: API changes needed for ellipsize

Decided not to change "layout()" function for now to avoid breaking the
interface. For now.

* chore: shape ellipsis

* feat: Ellipsize::Start

Since it can only have 1 line, it's easier to implement.

* DROPME: temporarily change rich-text for testing

* test(ellipsize): Testing Ellipsize::Start

Long text in small buffer should produce ellipsis glyphs

* fix: do not need font_system anymore

We moved ellipsis shaping elsewhere so no need to pass font_system to
layout function (which also was recreating a new one in the tests every
time making them take forever).

* feat: Ellipsize::End

* improv(ellipsize): use a single ellipsis shape

* improv: Ellipsie::End && Wrap::None

There is no need to layout the whole line if it's not going to fit.

* fix: mixed bidi text when Ellipsize::End && Wrap::None

* chore: clean up and simplify when line.RTL==span.RTL

* fix(ellipsize): last word is not (word_count -1) if iter().rev()

* refactor(layout): extract the layout algorithm to make it more readable

* improv(ellipsize): Ellipsize::Start && Wrap::None

we iterate in reverse and only layout what's going to be visible

* Revert: delete the previous approach of post processing ellipsis

* doc: explain the interaction between Ellipsize and Wrap

* chore: lower the scope

* feat: Ellipsize the last line of a paragraph

For now only the number of lines is supported

* fix: clear ellipsized field on visual lines

This was causing ellipsis to show on random lines

* chore: remove old tests

will add better tests soon

* chore: clean up changes from previous attempt

* fix: consider the ellipsis width when doing alignment

* feat(ellipsize): add `Height` limit to `Ellipsize`

* fix: ellipsize the start of the last line correctly

* fix: ellipsize at the start of mixed bidi lines

* feat: Ellipsize::Middle

* fix: consider ellipsize::middle when calculating alignment correction

* refactor: improve readability

* refactor: deduplicate "fit_glyphs"

* refactor: combine backward and forward layout into one (wip)

* fix: Backward works in the unified layout_spans

* chore: clean up

* fix: Ellipsize::Middle

* fix: handle large words in bidi boundaries

* chore: clean up and some refactoring

* fix: ellipsis is now the same level as the surrounding text

* fix: try to fit more when ellipsizing::middle

* improv: ellipsis now have the same level as the neighbors

This makes ellipsized RTL text inside a LTR line more readable.

before:

Hello سلام...خوبی؟
Hello خولی؟...سلام

* fix: some extra words were being rendered in Ellipsize::Middle

This was causing the last word (if it's not the same level as the rest)
to be rendered outside the buffer.

* test: a few test cases for ellipsize

* fix: assign the correct byte range to ellipsis

this should fix the panic when selecting or clicking on or near the
ellipsis in the editor.

tests/images/ellipsize_ltr_end_single_line.png

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