spec: for non-constant map keys, add reference to evaluation order section
spec: for non-constant map keys, add reference to evaluation order section

The section on map literals mentions constant map keys but doesn't say
what happens for equal non-constant map keys - that is covered in the
section on evaluation order. Added respective link for clarity.

Fixes #19689.

Change-Id: If9a5368ba02e8250d4bb0a1d60d0de26a1f37bbb
Reviewed-on: https://go-review.googlesource.com/38598
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

linux-on-ibm-z/go,josharian/go,ImJasonH/go,polyverse-security/go,codestation/go,CAFxX/go,linux-on-ibm-z/go,derekmarcotte/go,linux-on-ibm-z/go,vsekhar/elastic-go,Cofyc/go,Cofyc/go,akutz/go,cloudflare/go,akutz/go,linux-on-ibm-z/go,josharian/go,ImJasonH/go,polyverse-security/go,ImJasonH/go,cloudflare/go,vsekhar/elastic-go,polyverse-security/go,cloudflare/go,vsekhar/elastic-go,ImJasonH/go,polyverse-security/go,CAFxX/go,akutz/go,vsekhar/elastic-go,josharian/go,golang/go,Cofyc/go,codestation/go,josharian/go,derekmarcotte/go,nawawi/go,akutz/go,polyverse-security/go,derekmarcotte/go,polyverse-security/go,nawawi/go,nawawi/go,golang/go,nawawi/go,ImJasonH/go,CAFxX/go,vsekhar/elastic-go,derekmarcotte/go,CAFxX/go,golang/go,codestation/go,vsekhar/elastic-go,akutz/go,CAFxX/go,golang/go,codestation/go,golang/go,codestation/go,akutz/go,codestation/go,golang/go,Cofyc/go,CAFxX/go,nawawi/go,Cofyc/go,codestation/go,cloudflare/go,vsekhar/elastic-go,cloudflare/go,CAFxX/go,vsekhar/elastic-go,linux-on-ibm-z/go,Cofyc/go,josharian/go,golang/go,cloudflare/go,derekmarcotte/go,cloudflare/go,ImJasonH/go,polyverse-security/go,derekmarcotte/go,polyverse-security/go,Cofyc/go,josharian/go,golang/go,josharian/go,linux-on-ibm-z/go,josharian/go,cloudflare/go,linux-on-ibm-z/go,nawawi/go,nawawi/go,linux-on-ibm-z/go,nawawi/go,CAFxX/go,christopher-henderson/Go,akutz/go,akutz/go,derekmarcotte/go,ImJasonH/go,derekmarcotte/go,codestation/go,Cofyc/go,ImJasonH/go