Add some tests for TextBuffer::Reflow (microsoft#8715)

This is by no means comprehensive. It will be unmarked as draft when it
is more comprehensive.

This pull request adds some tests for resizing a TextBuffer and
reflowing its contents. Each test takes the form of an initial state and
a number of buffers of different sizes. The initial state is used to
seed the first TextBuffer, and the subsequent buffers are only used to
compare.

I manually reimplemented some of the DBCS logic to ensure that the
buffers contain _exactly_ what they're supposed to. I know this is
non-ideal. After some of the CharRow changes in microsoft#8446 land, this will
need to be updated.

There's a cool bit of TAEF gore in here: the IDataSource. An IDataSource
allows us to programmatically return test cases. It's a code-only
version of its support for parameterized tests of the form `Data:x = {0,
1, 2}` . 

The only downsides are...

1. It looks like COM (it is not using COM under the hood, just the COM
   ABI)
2. Property values must be returned as strings.

To best support rich test types, I used IDataSource to produce _a lit of
array indices_ and nothing more. The test is run once for array member,
and it is the test's responsibility to look up the object to which that
index refers.

Works great though! Each reflow test is its own unit, and a failure in
an earlier reflow test will not tank a later one.

.github/actions/spell-check/expect/expect.txt

@@ -1,8 +1,11 @@
+AAAAA
 AAAAAABBBBBBCCC
 AAAAABBBBBBBCCC
+AAAAABBBBBBCCC
 AAAAABCCCCCCCCC
 AAAAADCCCCCCCCC
 ABANDONFONT
+abcd
 ABCDEFGHIJKLMNO
 ABCG
 abf
@@ -129,6 +132,7 @@ backstory
 Batang
 baz
 Bazz
+BBBBBCCC
 BBBBCCCCC
 BBDM
 bbwe
@@ -290,6 +294,7 @@ CNTRL
 codebase
 Codeflow
 codepage
+codepath
 codepoint
 codeproject
 COINIT
@@ -755,6 +760,7 @@ FFrom
 FGCOLOR
 fgetc
 fgetwc
+FGHIJ
 fgidx
 FILEDESCRIPTION
 fileno
@@ -892,6 +898,9 @@ GFEh
 Gfun
 gfx
 gh
+GHIJK
+GHIJKL
+GHIJKLM
 gitfilters
 github
 gitlab
@@ -1198,6 +1207,7 @@ KILLFOCUS
 kinda
 KJ
 KLF
+KLMNO
 KLMNOPQRST
 KLMNOPQRSTQQQQQ
 KU
@@ -1244,6 +1254,7 @@ lld
 llvm
 llx
 LMENU
+LMNOP
 lnk
 lnkd
 lnkfile
@@ -1286,6 +1297,7 @@ LPFNADDPROPSHEETPAGE
 LPINT
 lpl
 LPMEASUREITEMSTRUCT
+LPMINMAXINFO
 lpmsg
 LPNEWCPLINFO
 LPNEWCPLINFOA
@@ -1317,6 +1329,7 @@ lsproj
 lss
 lstatus
 lstrcmp
+lstrcmpi
 LTEXT
 LTLTLTLTL
 ltype
@@ -1383,6 +1396,7 @@ mindbogglingly
 mingw
 minimizeall
 minkernel
+MINMAXINFO
 minwin
 minwindef
 Mip
@@ -1392,6 +1406,8 @@ mmcc
 MMCPL
 mmsystem
 MNC
+MNOPQ
+MNOPQR
 MODALFRAME
 modelproj
 MODERNCORE
@@ -1487,9 +1503,9 @@ Nls
 NLSMODE
 NOACTIVATE
 NOAPPLYNOW
-NOCOMM
 NOCLIP
 NOCOLOR
+NOCOMM
 NOCONTEXTHELP
 NOCOPYBITS
 nodiscard
@@ -1513,6 +1529,7 @@ NONPREROTATED
 nonspace
 NOOWNERZORDER
 NOPAINT
+NOPQRST
 noprofile
 NOREDRAW
 NOREMOVE
@@ -1866,6 +1883,7 @@ pythonw
 qi
 QJ
 qo
+QRSTU
 qsort
 queryable
 QUESTIONMARK
@@ -2213,6 +2231,7 @@ strrev
 strsafe
 strtok
 structs
+STUVWX
 STX
 stylecop
 SUA
@@ -2506,6 +2525,8 @@ utr
 uuid
 uuidof
 uuidv
+UVWX
+UVWXY
 UWA
 uwp
 uxtheme
@@ -2573,6 +2594,7 @@ VTRGBTo
 vtseq
 vtterm
 vttest
+VWX
 waaay
 waitable
 waivable
@@ -2812,6 +2834,8 @@ YVIRTUALSCREEN
 Yw
 YWalk
 yx
+YZ
+yzx
 Zc
 ZCmd
 ZCtrl
@@ -2822,9 +2846,3 @@ zsh
 zu
 zxcvbnm
 zy
-AAAAABBBBBBCCC
-BBBBBCCC
-abcd
-LPMINMAXINFO
-MINMAXINFO
-lstrcmpi

src/buffer/out/CharRow.hpp

@@ -81,9 +81,11 @@ class CharRow final
     // iterators
     iterator begin() noexcept;
     const_iterator cbegin() const noexcept;
+    const_iterator begin() const noexcept { return cbegin(); }
 
     iterator end() noexcept;
     const_iterator cend() const noexcept;
+    const_iterator end() const noexcept { return cend(); }
 
     UnicodeStorage& GetUnicodeStorage() noexcept;
     const UnicodeStorage& GetUnicodeStorage() const noexcept;