This reduces bootstrap cost for Windows customers, resolving the issue initially submitted as #12502 .

The `toolsrc` tree was extracted to https://github.com/microsoft/vcpkg-tool. `bootstrap.sh` was changed to download the right source tarball, extract, and build it. This was chosen over the previous attempt, a submodule, over concerns of accidentally destroying people's local modifications.

* [vcpkg formatting] correct the header regexes

* format

* [vcpkg] Format the C++ in the CI

* format the C++

* CR

==== Changes Related to manifests ====

* Add the `manifests` feature flag
  * This only says whether we look for a `vcpkg.json` in the cwd, not
    whether we support parsing manifests (for ports, for example)
* Changes to the manifests RFC
  * `"authors"` -> `"maintainers"`
  * `--x-classic-mode` -> `-manifests` \in `vcpkg_feature_flags`
  * reserve `"core"` in addition to `"default"`, since that's already
    reserved for features
  * Add a small helper note about what identifiers must look like
  * `<license-string>`: SPDX v3.8 -> v3.9
  * `"feature"."description"` is allowed to be an array of strings as well
  * `"version"` -> `"version-string"` for forward-compat with versions
    RFC
* Add the `--feature-flags` option
* Add the ability to turn off feature flags via passing
  `-<feature-flag>` to `VCPKG_FEATURE_FLAGS` or `--feature-flags`
* Add CMake toolchain support for manifests
  * Requires either:
    * a feature flag of `manifests` in either `Env{VCPKG_FEATURE_FLAGS}`
      or `VCPKG_FEATURE_FLAGS`
    * Passing the `VCPKG_ENABLE_MANIFESTS` option
  * The toolchain will install your packages to
    `${VCPKG_MANIFEST_DIR}/vcpkg_installed`.
* Add MSBuild `vcpkg integrate install` support for manifests
  * Requires `VcpkgEnableManifest` to be true
* `vcpkg create` creates a port that has a `vcpkg.json` instead of a
  `CONTROL`
* argparse, abseil, 3fd, and avisynthplus ports switched to manifest
  from CONTROL
* Add support for `--x-manifest-root`, as well as code for finding it if
  not passed
* Add support for parsing manifests!
* Add a filesystem lock!

==== Important Changes which are somewhat unrelated to manifests ====

* Rename `logicexpression.{h,cpp}` to `platform-expression.{h,cpp}`
* Add `PlatformExpression` type which takes the place of the old logic
  expression
  * Split the parsing of platform expressions from checking whether
    they're true or not
  * Eagerly parse PlatformExpressions as opposed to leaving them as
    strings
* Add checking for feature flag consistency
  * i.e., if `-binarycaching` is passed, you shouldn't be passing
    `--binarysource`
* Add the `Json::Reader` type which, with the help of user-defined
  visitors, converts JSON to your internal type
* VcpkgArgParser: place the switch names into a constant as opposed to
  using magic constants
  * In general update the parsing code so that this ^ works
* Add `Port-Version` fields to CONTROL files
  * This replaces the existing practice of
    `Version: <my-version>-<port-version>`

==== Smaller changes ====
* small drive-by cleanups to some CMake
  * `${_VCPKG_INSTALLED_DIR}/${VCPKG_TARGET_TRIPLET}` ->
    `${CURRENT_INSTALLED_DIR}`
  * Remove `-analyze` when compiling with clang-cl, since that's not a
    supported flag (vcpkg's build system)
  * Add a message about which compiler is detected by vcpkg's build
    system machinery
* Fix `Expected::then`
* Convert `""` to `{}` for `std::string` and `fs::path`, to avoid a
  `strlen` (additionally, `.empty()` instead of `== ""`, and `.clear()`)
* Add `Strings::strto` which converts strings to numeric types
* Support built-in arrays and `StringView` for `Strings::join`
* Add `operator<` and friends to `StringView`
* Add `substr` to `StringView`
* SourceParagraphParser gets some new errors

* [vcpkg] Add initial JSON support

This adds a JSON parser, as well as the amount of unicode support
required for JSON parsing to work according to the specification. In the
future, I hope to rewrite our existing XML files into JSON.

Additionally, as a drive-by, we've added the following:

* add /wd4800 to pragmas.h -- this is a "performance warning", for when
  you implicitly convert pointers or integers to bool, and shouldn't be
  an issue for us.
* Switched Parse::ParserBase to read unicode (as utf-8), as opposed to
  ASCII
* Building again under VCPKG_DEVELOPMENT_WARNINGS, yay!