erts: Fix is_map/1 spec
erts: Document map guard functions

* erlang:is_map/1
* erlang:map_size/1
Change encoding for XML files to utf-8

These are some files that were erronously missed earlier:

   erts/doc/src/time_correction.xml
   lib/crypto/doc/src/crypto_app.xml
   lib/snmp/doc/src/snmpa_mib_data.xml
   lib/snmp/doc/src/snmpa_mib_storage.xml
Remove "coding: utf-8" from test files

UTF-8 is now the default encoding and should no longer be
specified. These have probably been merged from maint earlier and the
coding statement was missed.

   lib/dialyzer/test/opaque_SUITE_data/src/modules/opaque_erl_scan.erl
   lib/diameter/test/diameter_codec_test.erl
   lib/ssh/test/ssh_unicode_SUITE.erl
Clarify the reference manual regarding source file encoding
compiler: Change Maps Core Format

Ex.

Instead of:

    M~{~<K,V>}~

The format is now:

    ~{~<K,V>|M}~

This also removes a shift/reduce warning.

The changes in core_pp now requires compiler-5.0 to compile
because of is_map/1 guard, i.e. a need for a compiler with Maps know-how.
erts: Handle literals in is_map/1
compiler: Guard BIF is_map/1 is pure
compiler: Support literal maps in cerl_clauses:match/2
compiler: Validate Map src

Reject all expressions that are known to fail.
Emit 'badarg' for those expressions.

Ex.

    []#{ a => 1}

Is not a valid map update expression.
compiler: Constant fold Maps that are safe

For updates of Map literals which may cause an error will be
determined in runtime, i.e. instructions are emitted for those
updates.

The changes in cerl now requires compiler-5.0 to compile because of
is_map/1 guard.
compiler: Change #c_map{var} to #c_map{arg}

Not only variables are allowed as arguments, the name should reflect that.

Change cerl Map argument interface
 * cerl:map_arg/1 is more suitable then cerl:map_val/1 in this case.
stdlib: Properly lint map key expressions

Only values are valid key expressions.
stdlib: Move map type to proper definition
stdlib: Accept Maps as Map keys
stdlib: Accept records as Map keys
stdlib: Test Map key linting

This will change in future release.
hipe: Properly identify map() type form terms
dialyzer: Do not native compile modules with Maps code

hipe:c/1 ignores '-compile(no_native).'
compiler: Transform M#{} to is_map(M)

Core should not understand M#{}

Instead transform M#{} to

    case _cor0 of
      <_cor1>
          when call 'erlang':'is_map'
                (_cor0) ->
          _cor1
      ( <_cor2> when 'true' ->
            primop 'match_fail'
                ('badarg')
        -| ['compiler_generated'] )
    end