GDScript: Add constant string support for POT generator

[dalexeev]

• Supersedes Make POT generator able to extract strings from binary operations #79998.

Use GDScriptAnalyzer to take constant string expressions into account when generating POTs.

const TEST_CONST = "test_const"
var test_var = "test_var"
print(tr("test_literal"))
print(tr("test_" + "concat"))
print(tr(TEST_CONST))
print(tr(test_var))

Before:

#: node.gd
msgid "test_literal"
msgstr ""

After:

#: node.gd
msgid "test_literal"
msgstr ""

#: node.gd
msgid "test_concat"
msgstr ""

#: node.gd
msgid "test_const"
msgstr ""

[adamscott]

Seems fine to me! Thanks @dalexeev !

[YuriSizov]

Thanks!