psh: Implement a parser for "quoted" commands

[gerard5]

Work in progress - do not merge.

I open this pull-request for discussion, maybe someone has already found better solution.

psh tests may fail because this change:

• uses quotes and spaces (tests may assume this is invalid use case)
• does not modify the command history buffer as it was originally with strtok, see description below.

Description

This pull-request adds support for quoted commands (single ' and double " quote), a quote inside quote requires an escape character \' or \" depending on the main type of quote used. Example:
"argument text \"inner quote\" 'other quote' end" or 'argument text \'inner quote\' "other quote" end'

The efects of this change:

Before the change (originally), the strtok() function was used, which modifies the command line stored in the command history, I implemented the function behaves similarly except that it allows the use of quotes. There is one, but ... now it uses a scratchpad where it stores a copy of the command line it is working on. This is necessary because the characters ", ' and \" \" are overwritten and the text is moved in the buffer, without the scratch buffer, the command history would be modified and the command would lose its meaning.

Support for \ without quotes is missing now, maybe I'll add this once I extend path completion to also support \ , so
e.g. cat /dir\ with\ spaces/file\ with\ spaces is not supported in this pull-request, instead use cat "/dir with spaces/file with spaces":

Motivation and Context

Need to support arguments that contains spaces and quotation marks.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: ia32-generic, nil-imxrt1176

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[kemonats]

A slightly simpler version of psh_stralloc()

char *psh_stralloc_t(char *oldstr, const char *str)
{
	char *newstr = strdup(str);
	
	if (newstr != NULL) {
		free(oldstr);
	}

	return newstr;
}

[gerard5]

I like it.

[kemonats]

Suggested change

	while (*ptr != '\0' && isspace(*ptr)) {
	ptr++;
	}
	while (isspace(*ptr) != 0) {
	ptr++;
	}

[kemonats]

This can be added to skip the psh_unescape() function call if there is no backaslash in quotation marks.
On top declare:

int need_unscape = 0;

Suggested change

	if (*ptr == '\0' || *(ptr - 1) != '\\') {
	break;
	}
	if (*ptr == '\0') {
	break;
	}
	if (*(ptr - 1) == '\\') {
	need_unscape = 1;
	}
	else {
	break;
	}

and return

return (need_unscape == 0) ? ret : psh_unescape(ret, quote);

[kemonats]

I see this was lost somewhere early.

Suggested change

	while (*ptr != '\0' && isspace(*ptr)) {
	ptr++;
	}

You skip the whitespace characters at the beginning of the function.