Overhaul Main Workflow Docs (dotnet#107415)

* Started the Quality Week work of improving the workflow docs.

* Made more progress on the general workflow README doc, as well as the CoreCLR one.

* Rephrased some things to make them roll off the tongue better, and fixed a couple spelling and grammatical mistakes.

* Basically finished the main  workflow README, and the CoreCLR building docs.

* Almost done with the CoreCLR building docs, finished the MacOS requirements one, and got far enough on the Windows requirements one.

* Finished the first pass on the Windows requirements doc.

* Finished the first pass of the Linux Environment Requirements.

* Finished the first pass of the Linux requirements doc.

* Made good progress on the 'Using Docker' new doc.

* Finished the first pass of the Using Docker doc.

* Initial merging of the new docs with the existing documentation.

* Improved the redaction of some sentences, improved some formatting, and fixed a few broken links.

* Forgot to commit a NativeAOT note.

* Removed the cross signs in the tables and added general info about cross-compiling to the general workflow introduction segment.

* Added some redaction improvements, and corrected a few misleading and/or outdated details.

* Linked the Workflow's README to the CoreCLR Building README.

* Added a few additional details, and improved some wording and phrasing to make the docs more friendly and clear as per received feedback.

* Fixed typo in the -DCLR_CMAKE_APPLE_DYSM=TRUE flags.