Move CmdPal API spec back to cmdpal/ directory (#48160)

Reverts 0819a62 / #46926

The cmdpal API is literally generated from this spec document. It needs
to live with the rest of the code to work correctly.

Docs for authoring cmdpal extensions are on
https://learn.microsoft.com/en-us/windows/powertoys/command-palette/extension-development,
and we should direct docs commentary there.

Author: zadjii-msft

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

@@ -105,7 +105,9 @@
 ^src/common/ManagedCommon/ColorFormatHelper\.cs$
 ^src/common/notifications/BackgroundActivatorDLL/cpp\.hint$
 ^src/common/sysinternals/Eula/
-^doc/devdocs/modules/cmdpal/initial-sdk-spec/list-elements-mock-002\.pdn$
+^src/modules/cmdpal/Tests/Microsoft\.CommandPalette\.Extensions\.Toolkit\.UnitTests/FuzzyMatcherComparisonTests.cs$
+^src/modules/cmdpal/Tests/Microsoft\.CommandPalette\.Extensions\.Toolkit\.UnitTests/FuzzyMatcherDiacriticsTests.cs$
+^src/modules/cmdpal/doc/initial-sdk-spec/list-elements-mock-002\.pdn$
 ^src/modules/cmdpal/ext/SamplePagesExtension/Pages/SampleMarkdownImagesPage\.cs$
 ^src/modules/cmdpal/Microsoft\.CmdPal\.UI/Settings/InternalPage\.SampleData\.cs$
 ^src/modules/cmdpal/Tests/Microsoft\.CmdPal\.Common\.UnitTests/.*\.TestData\.cs$