This pull request corrects an historical accident.
At some point in time, the set of Erlang terms was extended to include
maps, and at that time the `map()' type was also introduced to the
language as an easy, albeit quite coarse, way to declare map terms.
At some later point in time, the type language was extended with the
ability to declare _type associations_ in maps and also with a notation
to declare mandatory (:=) and optional (=>) type associations.

At that point in time, it should have been realized that the `map()'
type is nothing more than an alias (for `#{any() => any()}') instead
of being a _predefined_ type.  (The situation is analogous to e.g.
the `binary()' type being just an alias for `<<_:_*8>>'.)

This pull request corrects the documentation (the reference manual).

        * rickard/make-fixes-21/OTP-15551:
            Fix install phase in build system

            - Install of (mainly) documentation caused rebuild and
              modification of the source tree even when the source
              previously had been built. Also otp_patch_apply
              modified the source tree when updating documentation.
              This messed up the installation if installation was
              performed by another user than the user that originally
              built the system which not is an uncommon scenario.

            - Some documentation was installed by copying files
              instead of installing the files which caused faulty
              access rights on files.

            - The documentation was not properly updated when
              applying a patch using otp_patch_apply.

    * rickard/make-fixes-20/OTP-15551:
        Fix install phase in build system

        - Install of (mainly) documentation caused rebuild and
          modification of the source tree even when the source
          previously had been built. Also otp_patch_apply
          modified the source tree when updating documentation.
          This messed up the installation if installation was
          performed by another user than the user that originally
          built the system which not is an uncommon scenario.

        - Some documentation was installed by copying files
          instead of installing the files which caused faulty
          access rights on files.

        - The documentation was not properly updated when
          applying a patch using otp_patch_apply.

    * rickard/make-fixes-19/OTP-15551:
        Fix install phase in build system

        - Install of (mainly) documentation caused rebuild and
          modification of the source tree even when the source
          previously had been built. Also otp_patch_apply
          modified the source tree when updating documentation.
          This messed up the installation if installation was
          performed by another user than the user that originally
          built the system which not is an uncommon scenario.

        - Some documentation was installed by copying files
          instead of installing the files which caused faulty
          access rights on files.

        - The documentation was not properly updated when
          applying a patch using otp_patch_apply.

    * rickard/make-fixes-18/OTP-15551:
        Fix install phase in build system

        - Install of (mainly) documentation caused rebuild and
          modification of the source tree even when the source
          previously had been built. Also otp_patch_apply
          modified the source tree when updating documentation.
          This messed up the installation if installation was
          performed by another user than the user that originally
          built the system which not is an uncommon scenario.

        - Some documentation was installed by copying files
          instead of installing the files which caused faulty
          access rights on files.

        - The documentation was not properly updated when
          applying a patch using otp_patch_apply.

    * rickard/make-fixes-17/OTP-15551:
        Fix install phase in build system

        - Install of (mainly) documentation caused rebuild and
          modification of the source tree even when the source
          previously had been built. Also otp_patch_apply
          modified the source tree when updating documentation.
          This messed up the installation if installation was
          performed by another user than the user that originally
          built the system which not is an uncommon scenario.

        - Some documentation was installed by copying files
          instead of installing the files which caused faulty
          access rights on files.

        - The documentation was not properly updated when
          applying a patch using otp_patch_apply.

- Install of (mainly) documentation caused rebuild and
  modification of the source tree even when the source
  previously had been built. Also otp_patch_apply
  modified the source tree when updating documentation.
  This messed up the installation if installation was
  performed by another user than the user that originally
  built the system which not is an uncommon scenario.

- Some documentation was installed by copying files
  instead of installing the files which caused faulty
  access rights on files.

- The documentation was not properly updated when
  applying a patch using otp_patch_apply.